A switching power supply architecture for LED tubes suitable for large-size public displays

Abstract

The present invention discloses a switching power supply architecture for LED lamp tubes suitable for large-scale public displays. The architecture integrates the conventional two-way main power supply circuit 1 outputting 16V DC power and the main power supply circuit 2 outputting 24V DC power into a single main power supply circuit and a single transformer outputting two different voltages. This eliminates the conventional single main power supply circuit and reduces the cost of components and materials on the power supply board. The LED lamp tube adopts a high-voltage LED light string design. Under the condition of the same lamp power, the conduction current flowing through the Buck inductor and Buck N-channel MOS transistor is greatly reduced, thereby reducing the conduction loss within the step-down switching current control circuit. The quasi-resonant valley-turning MOS transistor is used to reduce the switching loss when the MOS transistor is turned on, thereby improving the backlight drive power conversion efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of switching power supplies for liquid crystal displays, and in particular to a switching power supply architecture suitable for LED lamps of large-scale public displays. Background Art

[0002] like Figure 1 As shown, the existing PD public LCD display product can be connected to the traditional high-power power board circuit function block diagram of the OPS plug-in computer. The power board uses a standby circuit to output 12V DC to power the main substrate circuit; the main power circuit 1 outputs 16V DC to power the OPS plug-in computer, Audio amplifier circuit, LCD panel T-CON circuit and USB circuits; the main power circuit 2 outputs 24V DC to power the Boost circuit. The 24V DC is boosted by the Boost circuit and the LED lamp current is controlled by the LED lamp total current control circuit, thereby achieving the control of the LCD display screen brightness. Features of this circuit: 1. Three independent circuits are used to output 12V, 16V, and 24V DC respectively to power the functional modules of each circuit equipment of the LCD display product. 2. The total current of the LED lamp is controlled, such as Figure 2 The 65-inch LED light tube uses 14 series and 6 parallels, that is, it uses 6 LED light strips, and each LED light strip is composed of 14 light-emitting diodes connected in series.

[0003] The existing technology uses three independent circuits to output 12V, 16V, and 24V DC power to power the functional modules of each circuit device of the LCD product. The circuit architecture is relatively complex and the cost of parts and materials is high. In addition, the control of the total current of the LED lamp has the following problems: Figure 2 As shown, (1) when Figure 2 In the LED tube, a short circuit occurs in a certain LED strip due to a problem with the raw materials of the LED (damage caused by ESD during the production process or poor process technology causing the electrical characteristics of the LED to decay) or long-term exposure to harsh external environments (for example, the product is used in the catering industry, such as hot pot restaurants, and is corroded by high-salinity water vapor for a long time, plus the hot and cold shock of switching on and off, causing the LED tube to fail). When a short circuit occurs in a certain LED strip, only 13 LEDs in the LED strip work, and 14 LEDs in the other 5 strips work. The working voltages at both ends of the 6 strips are the same. According to the working characteristics of the LED, the working current of the strip that has a short circuit will increase abnormally and significantly, exceeding the upper limit of the LED tube current specification, causing the remaining normally working LEDs in the LED strip to also short-circuit in a short period of time, eventually causing the LED strip to burn out or the backlight driver to generate over-temperature protection. (2) When Figure 2Due to problems with the raw materials of the LEDs, the internal resistance of one of the LED strips in the LED tube is too high during operation, causing the forward voltage to exceed the upper limit of the voltage specification. However, the operating voltage at both ends of the six strips is the same. Based on the operating characteristics of the LEDs, the operating current of the strip with the high internal resistance will be abnormally reduced, while the operating current of the remaining five strips will increase. The increase in current will increase the heating of the LEDs, causing the internal junction temperature of the LEDs to rise, accelerating product aging, and reducing the product life. Summary of the Invention

[0004] The object of the present invention is to provide a switching power supply architecture suitable for LED lamps of large-scale public displays.

[0005] The technical solution adopted in the present invention is:

[0006] A switching power supply architecture for LED lamps suitable for large-size public displays, comprising an EMI filter and bridge rectifier circuit, a PFC boost circuit, a power frequency large capacitor filter circuit, a standby circuit, a main power circuit, and a step-down switch current control circuit. The input end of the EMI filter and bridge rectifier circuit is connected to commercial AC power, and the output end of the EMI filter and bridge rectifier circuit is boosted by the PFC boost circuit and filtered by the power frequency large capacitor filter circuit to generate a first voltage DC power. The first voltage DC power is connected to the standby circuit and the main power circuit respectively by the output end of the power frequency large capacitor filter circuit, and is converted by the standby circuit to generate a second voltage DC power. The DC is used to power the main substrate circuit, and after voltage conversion by the main power supply circuit, a third voltage DC and a Vbus DC are generated. The voltage value of the Vbus DC is not less than the maximum operating voltage of the LED light string; the Vbus DC is used to power one or more high-voltage LED light strings; the output end of each high-voltage LED light string is connected to a step-down switching current control circuit, the step-down switching current control circuit is connected to the Vbus DC, and the step-down switching current control circuit receives a switching signal and a dimming signal provided by the main substrate circuit. The switching signal is used to control whether the step-down switching current control circuit is working, and the dimming signal is used to control the working current of the high-voltage LED light string.

[0007] Furthermore, the first voltage of direct current is 390V direct current; the second voltage of direct current is 12V direct current; and the third voltage of direct current is 16V direct current.

[0008] Furthermore, the voltage value of the Vbus direct current is 1.1 times the maximum operating voltage of the LED light string.

[0009] Furthermore, the main power supply circuit includes a main power supply primary side circuit, a transformer T1 and a feedback circuit; the main power supply primary side circuit is electrically connected to the primary side coil winding Np of the transformer T1, and the secondary side of the transformer T1 has Ns1 / Ns2 / Ns3 / Ns4 There are 4 coil windings, among which the dotted end of coil winding Ns1 is electrically connected to the positive end of rectifier diode D6, the non-dotted end of coil winding Ns1 is electrically connected to the dotted end of coil winding Ns2 and the positive end of rectifier diode D5, the non-dotted end of coil winding Ns2 and the dotted end of coil winding Ns3 are connected to the secondary side ground, the non-dotted end of coil winding Ns3 is electrically connected to the dotted end of coil winding Ns4 and rectifier diode D4, the non-dotted end of coil winding Ns4 is electrically connected to the positive end of rectifier diode D3, the negative ends of rectifier diodes D3 and D6 are connected to the positive end of the first filter capacitor C4 as the third voltage DC output end, the negative end of capacitor C4 is grounded, the negative ends of rectifier diodes D4 and D5 are connected to the positive end of the second filter capacitor C3 as the Vbus DC output end, and the negative end of capacitor C3 is grounded.

[0010] The third voltage DC output terminal and the Vbus DC output terminal are respectively connected to an input terminal of the feedback circuit, and the output terminal of the feedback circuit is connected to the primary side circuit.

[0011] Furthermore, the first voltage DC power is about 390V DC power, which is converted into voltage and electric energy by the primary side circuit control transformer T1 of the main power supply, and is full-wave rectified by the rectifier diodes D3 and D6 and filtered by the first filter circuit C4 to generate the third voltage DC power; after full-wave rectification by the rectifier diodes D4 and D5 and filtering by the second filter capacitor C3, the bus DC power is generated.

[0012] Furthermore, the third voltage DC output terminal supplies power to an external OPS plug-in computer device, an audio amplifier, a TCON circuit inside the liquid crystal panel, and a USB circuit.

[0013] Furthermore, the buck switch current control circuit includes a Buck inductor, a Buck N-channel MOS transistor, a freewheeling diode, a buck control circuit, a current sampling resistor, a valley detection circuit, and an energy storage capacitor connected in parallel with the corresponding high-voltage LED light string; the output end of the high-voltage LED light string is electrically connected to the negative electrode of the energy storage capacitor and the dotted end of the Buck inductor, the non-dotted end of the Buck inductor is electrically connected to the positive end of the freewheeling diode and the drain (Drain end) of the Buck N-channel MOS transistor, the negative end of the freewheeling diode is electrically connected to the positive electrode of the energy storage capacitor and the Vbus DC output end, the gate (Gate end) of the Buck N-channel MOS transistor is electrically connected to the buck control circuit, the source (Source end) of the Buck N-channel MOS transistor is electrically connected to one end of the current sampling resistor, the other end of the current sampling resistor is connected to the secondary ground, and the input end of the valley detection circuit is connected to the Buck. The drain of the N-channel MOS tube is electrically connected, and the output end of the valley detection circuit is electrically connected to the buck control circuit. The buck control circuit receives a switching signal from the main substrate circuit to control whether the circuit is working. The buck control circuit also receives a dimming signal from the main substrate circuit to correspondingly control the current of the high-voltage LED light string. The buck control circuit adopts a quasi-resonant working mode to detect the drain voltage of the Buck N-channel MOS tube through the valley detection circuit.

[0014] Furthermore, the buck switch current control circuit adopts quasi-resonant valley switching corresponding to the Buck N-channel MOS tube to significantly reduce the switching loss when the Buck N-channel MOS tube is turned on, thereby improving the power conversion efficiency of the LED lamp drive circuit.

[0015] Furthermore, as another embodiment, the gate drive method of the Buck N-channel MOS tube of the step-down switching current control circuit adopts the control of the PWM pulse width modulation square wave duty cycle Duty and the PWM pulse width modulation square wave operating frequency to achieve the control of the high-voltage LED lamp string operating current.

[0016] Furthermore, each high-voltage LED light string includes two or more LED light strips connected in series in sequence.

[0017] The present invention adopts the above technical solution, which has the following technical advantages over the existing technology: 1. It simplifies the circuit architecture of the traditional high-power power supply board of the external OPS plug-in computer and reduces the material cost of the power supply board. 2. When one or more light-emitting diodes inside a certain LED light strip in the LED lamp tube have a short circuit fault, the remaining light-emitting diodes that have not failed can still maintain a normal working current and work for a long time, that is, the service life of normal LED lamp tubes is improved. 3. When one or more light-emitting diodes inside a certain LED light strip in the LED lamp tube have a large conduction internal resistance when working, causing the forward conduction voltage to exceed the upper limit of the voltage specification during operation, the remaining normal light-emitting diodes can still maintain a normal working current and work for a long time, that is, the service life of normal LED lamp tubes is improved. 4. The conversion efficiency of the LED lamp tube driving circuit is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments;

[0019] Figure 1 This is a schematic diagram of the functional blocks of a traditional high-power power supply board circuit;

[0020] Figure 2 This is a schematic diagram of the traditional 65-inch LED tube structure using 14 series and 6 parallel connections;

[0021] Figure 3 This is a schematic diagram of a switching power supply architecture of an LED lamp tube suitable for large-scale public displays according to the present invention;

[0022] Figure 4 This is a schematic diagram of the existing 65-inch high-voltage LED light string structure;

[0023] Figure 5 Schematic diagram of the main power supply circuit, the buck switch current control circuit 1 and the buck switch current control circuit 2 of the present invention. Implementation Method

[0024] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0025] like Figures 3 to 5 As shown in one, the present invention discloses a switching power supply architecture suitable for LED lamp tubes of large-size public displays, the switching power supply comprising: EMI filtering and bridge rectifier circuit, PFC boost circuit, industrial frequency large capacitor filter circuit, standby circuit, main power supply circuit and step-down switch current control circuit.

[0026] The main power supply circuit uses a transformer to output two sets of different voltages. The first output voltage, such as 16V DC, supplies power to the back-end OPS plug-in computer, Audio amplifier circuit, LCD panel T-CON circuit, USB and other circuit devices; the second output voltage, such as a voltage of about 1.1 times the maximum operating voltage of the LED light string, supplies power to the LED lamp tube and controls the operating current of the LED lamp tube through the step-down switch current control circuit, thereby controlling the brightness of the LCD display screen.

[0027] The LED lamp tube is composed of one or more high-voltage LED light strings, which are composed of two or more LED light strips connected in series. For example, the LED lamp tube for a 55-inch LCD display product can be designed to consist of one high-voltage LED lamp tube, the LED lamp tube for a 65-inch LCD display product can be designed to consist of one or two high-voltage LED lamp tubes, the LED lamp tube for a 75-inch LCD display product can be designed to consist of two or three high-voltage LED lamp tubes, and the LED lamp tube for an 86-inch LCD display product can be designed to consist of three or four high-voltage LED lamp tubes.

[0028] Each high-voltage LED light string uses an independent step-down switching current control circuit to control the LED lamp current, thereby controlling the brightness of the LCD display. For example, if a 65-inch LCD product uses two high-voltage LED light strings, namely: high-voltage LED light string 1 and high-voltage LED light tube 2, the current of high-voltage LED light string 1 will be controlled by the corresponding step-down switching current control circuit 1; the current of LED light string 2 will be controlled by the corresponding step-down switching current control circuit 2.

[0029] The buck switching current control circuit 1 includes: Buck inductor L1, Buck N-channel MOS transistor Q1, freewheeling diode D1, buck control circuit 1, current sampling resistor Rs1, valley detection circuit 1 and energy storage capacitor C1 connected in parallel with the high-voltage LED light string 1; the output end of the high-voltage LED light string 1 is electrically connected to the negative electrode of the energy storage capacitor C1 and the dotted end of the Buck inductor L1, the non-dotted end of the Buck inductor L1 is electrically connected to the positive end of the freewheeling diode D1 and the drain end of the Buck N-channel MOS transistor Q1, the negative end of the freewheeling diode D1 is electrically connected to the positive end of the energy storage capacitor C1 and the input ends of the high-voltage LED light string 1 and the high-voltage LED light string 2, the gate end of the Buck N-channel MOS transistor Q1 is electrically connected to the buck control circuit 1, and the Buck The source terminal of the N-channel MOS transistor Q1 is electrically connected to one end of the current sampling resistor Rs1, the other end of which is connected to the secondary ground. The input terminal of the valley detection circuit 1 is electrically connected to the drain terminal of Q1, and the output terminal of the valley detection circuit 1 is electrically connected to the step-down control circuit 1. The step-down control circuit 1 receives a switching signal from the main substrate circuit to control whether the circuit is operating. The step-down control circuit 1 also receives a dimming signal from the main substrate circuit to control the current of the high-voltage LED light string 1. The step-down control circuit 1 adopts a quasi-resonant operating mode to detect the drain voltage of Q1 through the valley detection circuit 1.

[0030] Similarly, the output end of the high-voltage LED light string 2 adopts a step-down switching current control circuit 2 to control the current size of the LED light string 2 when it is working. The step-down switching current control circuit 2 is composed of: a Buck inductor L2, a Buck N-channel MOS transistor Q2, a freewheeling diode D2, a step-down control circuit 2, a current sampling resistor Rs2, a valley detection circuit 2 and an energy storage capacitor C2 connected in parallel with the high-voltage LED light string 2; the output end of the high-voltage LED light string 2 is electrically connected to the negative electrode of the energy storage capacitor C2 and the dotted end of the Buck inductor L2, the non-dotted end of the Buck inductor L2 is electrically connected to the positive end of the freewheeling diode D2 and the drain end of the Buck N-channel MOS transistor Q2, the negative end of the freewheeling diode D2 is electrically connected to the positive end of the energy storage capacitor C2 and the input ends of the high-voltage LED light string 1 and the high-voltage LED light string 2, the gate end of the Buck N-channel MOS transistor Q2 is electrically connected to the step-down control circuit 2, and the Buck The source terminal of the N-channel MOS transistor Q2 is electrically connected to one end of the current sampling resistor Rs2, the other end of which is connected to the secondary ground. The input terminal of the valley detection circuit 2 is electrically connected to the drain terminal of Q2, and the output terminal of the valley detection circuit 2 is electrically connected to the step-down control circuit 2. The step-down control circuit 2 receives a switching signal from the main substrate circuit to control whether the circuit is working. The step-down control circuit 2 also receives a dimming signal from the main substrate circuit to control the current of the high-voltage LED light string 2. The step-down control circuit 2 adopts a quasi-resonant operating mode to detect the drain voltage of Q2 through the valley detection circuit 2.

[0031] The gate drive method for Buck N-channel MOS transistors Q1 and Q2 in step-down switching current control circuits 1 and 2 controls the operating current of high-voltage LED light strings by controlling the duty cycle and operating frequency of the PWM square wave. This switching power supply features low component material costs, high energy conversion efficiency, and the ability to maintain constant operating current in the LEDs even when a short circuit or excessively high conduction resistance occurs in the high-voltage light string, ensuring long-term normal operation even when the forward voltage exceeds the upper voltage specification limit. This extends the life of the LEDs.

[0032] The specific working principle of the present invention is described in detail below:

[0033] Figure 3 This is an example of a switching power supply of the present invention, which is suitable for an external OPS plug-in computer and has a new LED lamp drive circuit for a 65-inch public display that extends the service life of the LED lamp. The switching power supply includes: an EMI filter and bridge rectifier circuit, a PFC boost circuit, an industrial frequency large-capacitor filter circuit, a standby circuit, a main power supply circuit, a buck switch current control circuit 1, and a buck switch current control circuit 2.

[0034] After the mains AC power passes through the EMI filter and bridge rectifier circuit, it is boosted by the PFC boost circuit and filtered by the power frequency large capacitor filter circuit to generate a DC power of about 390V. After the standby circuit performs voltage conversion, it generates a 12V DC power to power the main substrate circuit inside the LCD product. After the main power circuit performs voltage conversion on the 390V DC power, it generates a 16V DC power to power the external OPS plug-in computer equipment, Audio amplifier, TCON circuit inside the LCD panel, USB and other circuit equipment. After the main power circuit performs voltage conversion on the 390V DC power, it generates a Vbus DC power. The Vbus DC power is generally designed to be about 1.1 times the maximum operating voltage of the LED light string. For example, taking a 65-inch LED lamp as an example (reference Figure 4 ), the 65-inch LED tube uses 6 LED light strips, each LED light strip is composed of 14 light-emitting diodes connected in series, while high-voltage LED light string 1 and high-voltage LED light string 2 are respectively composed of 3 LED light strips connected in series.

[0035] If the maximum operating voltage of each light-emitting diode is 3.0V @ 500mA, the maximum operating voltage of a 65-inch LED light string is approximately 3.0V*14*3=126V. Therefore, a Vbus DC voltage of 139V can be designed. This Vbus DC voltage is provided by the input terminals of high-voltage LED light strings 1 and 2 to the light strings for operation. The output terminals of high-voltage LED light strings 1 and 2 are electrically connected to step-down switching current control circuits 1 and 2, respectively, to control the operating currents of high-voltage LED light strings 1 and 2. Step-down switching current control circuits 1 and 2 receive switching signals from the main substrate circuit to control their operation. Step-down switching current control circuits 1 and 2 also receive dimming signals from the main substrate circuit to control the operating currents of high-voltage LED light strings 1 and 2, thereby controlling the brightness of the LCD display.

[0036] like Figure 5The circuit function diagram is further expanded for the main power supply circuit, step-down switch current control circuit 1 and step-down switch current control circuit 2. The main power supply circuit includes: the main power supply primary side circuit, feedback circuit, transformer T1, C3 and C4 output filter capacitors, D3 and D4 and D5 and D6 output rectifier diodes; the main power supply primary side circuit performs voltage conversion through transformer T1, performs full-wave rectification through D3 and D6 rectifier diodes, and is filtered through C4 output filter capacitor to generate a 16V DC power supply for external OPS plug-in computer equipment, Audio amplifier, TCON circuit inside LCD panel, USB and other circuits; the main power supply primary side circuit performs voltage conversion through transformer T1, performs full-wave rectification through D4 and D5 rectifier diodes, and is filtered through C3 output filter capacitor to generate a Vbus DC power of about 1.1 times the maximum operating voltage of the LED light string.

[0037] If the maximum operating voltage of each LED is 3.0V at a 500mA operating current, the maximum operating voltage of a 65-inch LED light string is approximately 3.0V*14*3=126V. Therefore, a Vbus of 139V DC can be designed. This Vbus DC power is supplied to the light strings by the input terminals of high-voltage LED light strings 1 and 2. The negative terminals of rectifier diodes D4 and D5 are electrically connected to the input terminals of high-voltage LED light strings 1 and 2.

[0038] The output end of the high-voltage LED light string 1 controls the operating current of the LED light string through a step-down switching current control circuit 1. The step-down switching current control circuit 1 includes: a Buck inductor L1, a Buck N-channel MOS tube Q1, a freewheeling diode D1, a step-down control circuit 1, a current sampling resistor Rs1, and an energy storage capacitor C1 connected in parallel with the high-voltage LED light string 1; the output end of the high-voltage LED light string 1 is electrically connected to the negative electrode of the energy storage capacitor C1 and the dotted end of the Buck inductor L1, the non-dotted end of the Buck inductor L1 is electrically connected to the positive end of the freewheeling diode D1 and the drain end of the Buck N-channel MOS tube Q1, the negative end of the freewheeling diode D1 is electrically connected to the positive end of the energy storage capacitor C1 and the input ends of the high-voltage LED light string 1 and the high-voltage LED light string 2, the gate end of the Buck N-channel MOS tube Q1 is electrically connected to the step-down control circuit 1, and the Buck The source terminal of the N-channel MOS transistor Q1 is electrically connected to one end of the current sampling resistor Rs1, the other end of which is connected to the secondary ground. The input terminal of the valley detection circuit 1 is electrically connected to the drain terminal of Q1, and the output terminal of the valley detection circuit 1 is electrically connected to the step-down control circuit 1. The step-down control circuit 1 receives a switching signal from the main substrate circuit to control whether the circuit is operating. The step-down control circuit 1 also receives a dimming signal from the main substrate circuit to control the current of the high-voltage LED light string 1. The step-down control circuit 1 adopts a quasi-resonant operating mode to detect the drain voltage of Q1 through the valley detection circuit 1.

[0039] Similarly, the output end of the high-voltage LED light string 2 adopts a step-down switching current control circuit 2 to control the operating current of the LED light string 2. The step-down switching current control circuit 2 is composed of: a Buck inductor L2, a Buck N-channel MOS transistor Q2, a freewheeling diode D2, a step-down control circuit 2, a current sampling resistor Rs2, and an energy storage capacitor C2 connected in parallel with the high-voltage LED light string 2. The output end of the high-voltage LED light string 2 is electrically connected to the negative electrode of the energy storage capacitor C2 and the dotted end of the Buck inductor L2, the non-dotted end of the Buck inductor L2 is electrically connected to the positive end of the freewheeling diode D2 and the drain end of the Buck N-channel MOS transistor Q2, the negative end of the freewheeling diode D2 is electrically connected to the positive end of the energy storage capacitor C2 and the input ends of the high-voltage LED light string 1 and the high-voltage LED light string 2, the gate end of the Buck N-channel MOS transistor Q2 is electrically connected to the step-down control circuit 2, and the Buck The source terminal of the N-channel MOS transistor Q2 is electrically connected to one end of the current sampling resistor Rs2, the other end of which is connected to the secondary ground. The input terminal of the valley detection circuit 2 is electrically connected to the drain terminal of Q2, and the output terminal of the valley detection circuit 2 is electrically connected to the step-down control circuit 2. The step-down control circuit 2 receives a switching signal from the main substrate circuit to control whether the circuit is working. The step-down control circuit 2 also receives a dimming signal from the main substrate circuit to control the current of the high-voltage LED light string 2. The step-down control circuit 2 adopts a quasi-resonant operating mode to detect the drain voltage of Q2 through the valley detection circuit 2.

[0040] The buck switching current control circuit 1 and the buck switching current control circuit 2 of the present invention use quasi-resonant valley-turned Buck N-channel MOS transistors Q1 and Q2. The advantage of Q1 and Q2 MOS transistors being turned on in the quasi-resonant valley is that they can significantly reduce the switching loss of the switch MOS transistors when turning on, thereby improving the power conversion efficiency of the LED lamp drive circuit. The circuit adjusts the operating frequency of the Buck N-channel MOS transistor according to the voltage across the Buck inductor to achieve constant control of the operating current of the LED light string. If the transformer is designed to output a voltage Vbus of 139V to the high-voltage light string, the operating voltage VLB of the high-voltage light string at both ends is 126V when the operating current I is 500mA, and the inductance of the Buck inductors L1 and L2 is L: 0.2mH, then a voltage of 13V will appear on the buck switching current control circuit. At this time, the inductor operating frequency

[0041] F1=(Vbus-VLB)*VLB / (2*L*I*Vbus)

[0042] =(139V-126V)*126V / (2*0.2mH*500mA*139V)=58.9KHZ

[0043] When two LEDs in a high-voltage light string are short-circuited,

[0044] VLB=3.0V*(14*3-2)=120V, then a voltage of 19V will fall on the step-down switch current control circuit. At this time, the inductor operating frequency

[0045] F2=(139V-120V)*120V / (2*0.2mH*500mA*139V)=82KHZ

[0046] That is, when a light-emitting diode in the high-voltage light string is short-circuited, the light string voltage drops, the voltage across the Buck inductor rises, and the step-down switch current control circuit automatically adjusts and increases the step-down operating switching frequency to achieve the goal of keeping the operating current of the high-voltage LED light string unchanged.

[0047] Similarly, when one or more LEDs within a high-voltage LED tube exhibit excessive internal resistance, causing the forward voltage to exceed the upper voltage specification limit, the VLB voltage increases, the voltage across the Buck inductor decreases, and the step-down switching current control circuit automatically adjusts and reduces the step-down switching frequency, maintaining the operating current of the high-voltage LED string. Specifically, when a short circuit in a high-voltage LED string causes the operating voltage to drop, or when excessive internal resistance causes the forward voltage to exceed the upper voltage specification limit, causing the operating voltage to rise, the LED string operating current remains constant, ensuring that the remaining LEDs in the string continue to operate normally, thus extending the service life of a normal LED tube. This overcomes the problem of traditional total current control, where a short circuit in a light strip can cause the remaining normally operating LEDs to short-circuit within a short period of time.

[0048] The traditional two-way main power supply circuit 1 outputting 16V DC and main power supply circuit 2 outputting 24V DC are integrated into one main power supply circuit and one transformer outputting two different voltages. This eliminates the traditional main power supply circuit and reduces the parts and material costs on the power supply board.

[0049] The LED tubes utilize a high-voltage LED string design. Under the same tube power conditions, the on-current flowing through the Buck inductor and Buck N-channel MOSFET is significantly reduced, minimizing conduction losses within the buck switch current control circuit. The use of a quasi-resonant valley-turning MOSFET reduces switching losses when the Buck N-channel MOSFET is turned on, thereby improving the backlight driver power conversion efficiency.

[0050] The technical features of the novel switching power supply circuit for liquid crystal display products of the present invention are: low component material cost, high power conversion efficiency, and the ability to control the operating current of the LED lamp tube to remain unchanged and operate normally for a long time even when a short circuit occurs in the light-emitting diode in the high-voltage lamp string or the internal resistance of the working conduction is relatively large, so that when the forward conduction voltage exceeds the upper limit of the voltage specification during operation, the LED lamp tube can still be operated normally for a long time, thereby extending the service life of the LED lamp tube.

[0051] Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. In the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present application is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

Claims

1. A switching power supply architecture for LED tube lamps suitable for large-scale public displays, characterized by: It includes an EMI filter and bridge rectifier circuit, a PFC boost circuit, an industrial frequency large capacitor filter circuit, a standby circuit, a main power supply circuit and a step-down switch current control circuit. The input end of the EMI filter and bridge rectifier circuit is connected to the commercial AC power. The output end of the EMI filter and bridge rectifier circuit is boosted by the PFC boost circuit and filtered by the industrial frequency large capacitor filter circuit to generate a first voltage DC power. The first voltage DC power is connected to the standby circuit and the main power supply circuit respectively by the output end of the industrial frequency large capacitor filter circuit. After voltage conversion by the standby circuit, the second voltage DC power is generated to power the main substrate circuit. After voltage conversion, the source circuit generates a third voltage DC power and a Vbus DC power. The voltage value of the Vbus DC power is not less than the maximum operating voltage of the LED light string. The Vbus DC power supplies power to one or more high-voltage LED light strings. The output end of each high-voltage LED light string is connected to a step-down switching current control circuit. The step-down switching current control circuit is connected to the Vbus DC power. The step-down switching current control circuit receives a switching signal and a dimming signal provided by the main substrate circuit. The switching signal is used to control whether the step-down switching current control circuit is operating, and the dimming signal is used to control the operating current of the high-voltage LED light string. The main power supply circuit includes a main power supply primary side circuit, a transformer T1 and a feedback circuit; the main power supply primary side circuit is electrically connected to the primary side coil winding Np of the transformer T1, and the secondary side of the transformer T1 has four coil windings Ns1, Ns2, Ns3 and Ns4, wherein the dotted end of the coil winding Ns1 is electrically connected to the positive end of the rectifier diode D6, the non-dotted end of the coil winding Ns1 is electrically connected to the dotted end of the coil winding Ns2 and the positive end of the rectifier diode D5, the non-dotted end of the coil winding Ns2 is electrically connected to the positive end of the coil winding Ns3 The dotted end is connected to the secondary side ground, the non-dotted end of the coil winding Ns3 is electrically connected to the dotted end of the coil winding Ns4 and the rectifier diode D4, the non-dotted end of the coil winding Ns4 is electrically connected to the positive end of the rectifier diode D3, the negative ends of the rectifier diodes D3 and D6 are connected to the positive end of the first filter capacitor C4 as the third voltage DC output end, the negative end of the first filter capacitor C4 is grounded, the negative ends of the rectifier diodes D4 and D5 are connected to the positive end of the second filter capacitor C3 as the Vbus DC output end, and the negative end of the second filter capacitor C3 is grounded.

2. The switching power supply architecture for LED lamps suitable for large-scale public displays according to claim 1, characterized in that: The first voltage DC is 390V DC; the second voltage DC is 12V DC; and the third voltage DC is 16V DC.

3. The switching power supply architecture for LED lamps suitable for large-scale public displays according to claim 1, characterized in that: The voltage of the Vbus DC power supply must be at least 1.1 times the maximum operating voltage of the LED light string.

4. The switching power supply architecture for LED lamps suitable for large-scale public displays according to claim 1, characterized in that: The third voltage DC output terminal and the Vbus DC output terminal respectively correspond to an input terminal of the feedback circuit, and the output terminal of the feedback circuit is connected to the primary side circuit; the first voltage DC is 390V DC, which is converted into voltage and electric energy by the primary side circuit of the main power supply by controlling the transformer T1, and is full-wave rectified by the rectifier diodes D3 and D6, and filtered by the first filter capacitor C4 to generate the third voltage DC; after full-wave rectification by the rectifier diodes D4 and D5, and filtering by the second filter capacitor C3, the bus DC is generated.

5. The switching power supply architecture for LED lamps suitable for large-scale public displays according to claim 1, characterized in that: The third voltage DC power is used to power external OPS plug-in computer devices, audio amplifiers, TCON circuits inside the LCD panel, and USB circuit devices.

6. The switching power supply architecture for LED lamps suitable for large-scale public displays according to claim 1, characterized in that: The buck switch current control circuit includes a Buck inductor, a Buck N-channel MOS transistor, a freewheeling diode, a buck control circuit, a current sampling resistor, a valley detection circuit, and an energy storage capacitor connected in parallel with the corresponding high-voltage LED light string; the output end of the high-voltage LED light string is electrically connected to the negative electrode of the energy storage capacitor and the dotted end of the Buck inductor, the non-dotted end of the Buck inductor is electrically connected to the positive end of the freewheeling diode and the drain of the Buck N-channel MOS transistor, the negative end of the freewheeling diode is electrically connected to the positive electrode of the energy storage capacitor and the Vbus DC output end, the gate of the Buck N-channel MOS transistor is electrically connected to the buck control circuit, the source of the Buck N-channel MOS transistor is electrically connected to one end of the current sampling resistor, the other end of the current sampling resistor is connected to the secondary ground, and the input end of the valley detection circuit is connected to the Buck The drain of the N-channel MOS tube is electrically connected, and the output end of the valley detection circuit is electrically connected to the buck control circuit. The buck control circuit receives a switching signal from the main substrate circuit to control whether the circuit is working. The buck control circuit also receives a dimming signal from the main substrate circuit to correspondingly control the current of the high-voltage LED light string. The buck control circuit adopts a quasi-resonant working mode to detect the drain voltage of the Buck N-channel MOS tube through the valley detection circuit.

7. The switching power supply architecture for LED lamps suitable for large-scale public displays according to claim 6, characterized in that: The buck switch current control circuit adopts quasi-resonant valley switching corresponding to the Buck N-channel MOS tube to significantly reduce the switching loss when the Buck N-channel MOS tube is turned on, thereby improving the power conversion efficiency of the LED lamp drive circuit.

8. The switching power supply architecture for LED lamps suitable for large-scale public displays according to claim 1, characterized in that: The gate drive mode of the Buck N-channel MOS tube of the step-down switching current control circuit adopts the control of the duty cycle of the PWM pulse width modulation square wave and the operating frequency of the PWM pulse width modulation square wave to control the operating current of the high-voltage LED light string.

9. The switching power supply architecture for LED lamps suitable for large-scale public displays according to claim 1, characterized in that: Each high-voltage LED light string includes two or more LED light strips connected in series.

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