Cold cathode florescent lamp converter, control method thereof and control module thereof

Abstract

The invention discloses a cold cathode florescent lamp converter, a control method thereof and a control module thereof. The cold cathode florescent lamp converter comprises a driving circuit, a controller, a detector and a frequency reduction circuit. The driving circuit is used for driving a cold cathode florescent lamp, the controller generates a control signal to control the driving circuit, the frequency of the control signal is in inverse proportion to the output / input gain ratio of the driving circuit, and the duty ratio of the control signal is correspondingly reduced when the output / input gain ratio is over a preset value. The detector is used for detecting the duty ratio of the control signal; and if detecting that the duty ratio is greater than an upper limit value, the detector sends a trigger signal to the frequency reduction circuit coupled to the detector and the controller, and the frequency reduction circuit receives the trigger signal and gradually regulates and reduces the frequency of the control signal till the duty ratio is smaller than the upper limit value according to the trigger signal. Therefore, the effect of automatically and gradually regulating and reducing the frequency of the control signal is achieved.

Description

technical field [0001] The invention relates to a control method of a converter, in particular to a control method of a cold cathode lamp converter. Background technique [0002] The backlights of current liquid crystal displays are roughly divided into cold cathode fluorescent lamps (ColdCathod Fluorescent Lamp, CCFL) and light-emitting diodes (LEDs). Among them, the backlight of LCD displays with cold cathode fluorescent lamps needs to be equipped with a device to convert the current from DC to AC. The high-voltage converter (also known as the lamp) is used to light the cold cathode lamp of the panel. At present, after the cold-cathode lamps are lit, the current converters used in the current industry use a fixed frequency to control the power switch in the converter, and adjust the output power by controlling the conduction duty ratio of the power switch. . [0003] refer to figure 1 , is a common push-pull (Push-Pull) parallel resonant converter, with a DC power suppl...

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Problems solved by technology

However, when the duty cycle of the power switch increases to a preset maximum value, such as 45%, this method can no longer be used to increase a larger output current, and if the liquid crystal display is equipped with an overpower protection device, When the duty cycle of the power switch reaches the maximum value, the over-power protection device will turn off the entire cold-cathode lamp, that is, the over-power protection device will not be long after the cold-cathode lamp is lit due to the occupation of the power switch. The cold cathode lamp is turned off when the empty ratio reaches the maximum value. This phenomenon is definitely not what the designer expected. Therefore, in order to solve the above problem, the existing method is to install an over-power protection device regardless of whether the display is installed, because the control can no longer be adjusted. The duty cycle of the signal, so the existing method is to manually adjust the frequency of the control signal to increase the output current and restore the original output / input gain ratio. However, manual adjustment is not only time-consuming but also costly. Therefore, there are still improvements in the existing methods

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