Light emitting diode driving circuit

Abstract

The invention relates to a light emitting diode driving circuit for driving a plurality of light emitting diode chains. The light emitting diode driving circuit comprises a plurality of constant current circuits and a plurality of short-circuit protection circuits; a transistor and a detection resistor in each constant current circuit are coupled in series between the output end and the ground end of a corresponding light emitting diode chain; and when the constant current circuits work normally, by comparing a reference voltage with a detection voltage generated by the detection resistor, a feedback circuit in each constant current circuit outputs a signal to control the size of current passing through the transistor to achieve constant current control; in addition, each short-circuit protection circuit is coupled with the output end of the corresponding light emitting diode chain and the corresponding constant current circuit and is used for outputting a short circuit signal to cut off the transistor of the corresponding constant current circuit to turn off the corresponding light emitting diode chain when the voltage of the output end of the corresponding light emitting diode chain reaches a preset voltage and the voltage of the input end of a short circuit signal generation circuit in the short-circuit protection circuit reaches a preset voltage.

Description

technical field [0001] The invention relates to a light-emitting diode drive circuit, in particular to a light-emitting diode drive circuit with a short-circuit protection function. Background technique [0002] Today's liquid crystal display products have gradually begun to use a light source composed of light-emitting diodes as a backlight source. see figure 1 , figure 1 It is a circuit diagram of an existing LED driving circuit 10 . The LED driving circuit 10 is used to drive a plurality of LED light strings 22 , wherein each LED light string 22 includes a plurality of LED light strings 26 coupled in series. A light source composed of a plurality of LED light strings 22 can be applied as a backlight light source for liquid crystal display products. Each LED light string 22 has an input end 221 and an output end 223 respectively, and the input ends 221 of all LED light strings 22 are coupled to a DC voltage output by a DC / DC converter 24 . The LED drive circuit 10 can...

AI Technical Summary

Problems solved by technology

[0005] When at least one LED 26 of a plurality of LED lamp strings 22 is short-circuited, the voltage of the output terminal 223 of the corresponding LED lamp string 22 that is short-circuited will increase, and when the voltage of the output terminal 223 exceeds a predetermined voltage, the voltage regulator The diode 152 will collapse, and when the voltage at the input terminal of the short-circuit signal generating circuit 153 reaches a preset voltage, the internal transistor of the short-circuit signal generating circuit 153 will be turned on, and the output terminal of the short-circuit signal generating circuit 153 will output a low level signal ( Equivalent to outputting a short-circuit signal) pull the switch control signal On / Off output from the mainboard circuit 12 to a low level, and the low level switch control signal On / Off outputs a signal through the switch control circuit 13 to control the switch 11 to cut off, so that The DC voltage Vcc no longer supplies power to all the constant current circuits 14, so all the constant current circuits 14 do not work, and then all the light-emitting diode strings 22 are turned off. At this time, the liquid crystal display product will not be able to display the picture

[0006] Such liquid crystal display products may have the following problems: first, when people use liquid crystal color TVs to watch exciting programs or use multimedia liquid crystal displays for meetings or studies, suddenly the light-emitting diodes in the light-emitting diode strings in the liquid crystal panel are short-circuited. Cause the short circuit protection circuit to operate and make the entire LCD panel screen not bright, which may cause users to have great complaints about such LCD products

Second, due to the failure of the LCD panel, it is usually not possible to repair it at the LCD product design manufacturer, but it usually has to be sent to the original LCD panel factory for repairs, and some LCD panels are produced in foreign countries, which will cause a long maintenance period. If the warranty period is exceeded, the user will need to spend a higher maintenance fee, which is unacceptable to the user

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