Power circuit of backlight display system

Abstract

The invention relates to a power circuit of a backlighting display system, which can realize the normal start and current balance of a plurality of luminous bodies CCFL or EEFL in parallel connection and series connection in operation. The adopted technical proposal is to utilize the backlighting source to provide a luminous circuit with high voltage power. The luminous circuit includes a plurality of luminous bodies and a plurality of mutual inductors. Each of the luminous bodies is in series connection with the corresponding mutual inductor primary coil and switches in the backlighting source to form a loop. An in phase end of the primary mutual inductor secondary coil is connected an out phase end of the adjacent mutual inductor secondary coil. By the same token, the in phase end of the last mutual inductor secondary coil is connected with the out phase end of the primary mutual inductor secondary coil and all mutual inductor secondary coils are in series connection. Because the parameter of every mutual inductor is the same, the secondary coils of every mutual inductor are in series connection in operation and the current in the mutual inductor primary coil is the same, the current of all luminous bodies is the same. Thereby, the invention can solve the current balance problem of a plurality of luminous bodies in parallel connection in operation.

Description

technical field [0001] The invention relates to a power supply circuit of a backlight display system, in particular to a backlight circuit utilizing CCFL or EEFL as a backlight source. Background technique [0002] In the prior art, cold cathode fluorescent lamps (CCFL) or external electrode fluorescent lamps (EEFL) are used as the backlight in the backlight circuit of liquid crystal display (LCD) products. Since CCFL and EEFL have high voltage at start-up and low voltage at normal operation, the start-up voltage for CCFL usually requires more than 1000V, while the normal work voltage is usually only between 300V and 800V. If multiple CCFLs are directly connected in parallel, an additional When the voltage above 1000V is started, due to the performance difference between each CCFL, only one CCFL can start to emit light. After this CCFL is started, the applied voltage drops below 800V, and other CCFLs cannot be started. Body, but the required start-up voltage is higher, and ...

AI Technical Summary

Problems solved by technology

Since CCFL and EEFL have high voltage at start-up and low voltage at normal operation, for CCFL, the start-up voltage usually requires more than 1000V, while the normal work voltage is usually only between 300V and 800V. If multiple CCFLs are directly connected in parallel, an additional When the voltage above 1000V is started, due to the performance difference between each CCFL, only one CCFL can start to emit light. After this CCFL is started, the applied voltage drops below 800V, and other CCFLs cannot be started. body, but the required start-up voltage is higher, and the normal operating voltage is relatively increased. Therefore, in the prior art, it is necessary to increase the capacitance (such as figure 1 ) or a transformer (such as figure 2 ) circuit to start all parallel CCFLs or EEFLs, there is no circuit in the prior art where the light emitters work in series

[0003] figure 1 It is a schematic diagram of a circuit using CCFL as an LCD backlight source in the prior art. In this circuit, a capacitor is connected in series between each CCFL and the backlight power supply. Due to the voltage division effect of the capacitor, when the CCFL is started and the CCFL is working normally, there is a voltage across the capacitor. Voltage, the voltage of the capacitor plus the operating voltage of the CCFL during normal operation can start other CCFLs in turn, but due to the difference in the performance of each CCFL, the current flowing through each CCFL is unbalanced. When the current error is too large, some of the CCFLs The current flowing through is too large, which reduces the life of CCFL, while the current of some other CCFLs is too small, and the CCFL cannot reach the designed brightness

[0004] figure 2 Another structural circuit schematic diagram of using CCFL as the LCD backlight source in the prior art, in figure 1 On the basis of this method, a transformer is added to each CCFL circuit, and the transformer is used to boost the voltage of each CCFL lamp. Although this technical solution solves the technical problems that CCFL cannot be directly connected in parallel and the working current is unbalanced, each transformer must be connected with the The corresponding CCFL is used together, the circuit adjustment is difficult, and the compatibility is poor. When replacing the CCFL, the circuit needs to be re-adjusted

This technical solution has the advantages of high cost and inconvenient use and maintenance. With the increase of the number of CCFLs, the circuit impedance increases, and the increase of temperature leads to the decrease of product life and the increase of power loss.

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