CN201248185Y

CN201248185Y - Inverter for current error protection cold-cathode tube

Info

Publication number: CN201248185Y
Application number: CNU2008200956388U
Authority: CN
Inventors: 温学礼
Original assignee: SHENZHEN DATA-POWER ELECTRONICS Co Ltd
Current assignee: SHENZHEN DATA-POWER ELECTRONICS Co Ltd
Priority date: 2008-07-18
Filing date: 2008-07-18
Publication date: 2009-05-27
Anticipated expiration: 2018-07-18

Abstract

The utility model discloses an inverter used for a current error protecting cold-cathode tube and aims at causing a liquid crystal screen lamp to have protection function under the situation of current error, lamp leakage and poor contact so as to improve the image quality and the safety of a liquid crystal screen. Signals outputted by the control chip of the inverter used for a current error protecting cold-cathode tube is transmitted to a booster transformer through an MOS transistor, a cold cathode fluorescence lamp of the liquid crystal screen is driven, the signals fed back by the cold cathode fluorescence lamp are transmitted to the control chip through a feedback circuit, two ends of the output pole of the booster transformer are connected in parallel with a current error protecting sampling circuit, and the sampled signals are transmitted to the control chip through a protective circuit. Compared with the prior art, the utility model adopts a common capacitor and a detecting transformer neutral-point voltage shift for protective detection and achieves CCFL (cold cathode fluorescence lamp) current error protection, open circuit protection, single-channel output earthing short-circuit protection, single-lamp short-circuit protection and LCC protection, thereby being safe, reliable, and simple in structure.

Description

Current error protection cold-cathode tube-use inverter

Technical field

The utility model relates to a kind of cold cathode lamp of liquid crystal display screen, the inverter that particularly a kind of cold cathode lamp is used.

Background technology

Present liquid crystal display screen mainly adopts passive light-emitting mode, and just liquid crystal itself is not luminous, and the liquid crystal display screen light source mainly is by cold-cathode fluorescence lamp CCFL lamp luminescence, and CCFL lamp luminescence quality directly influences the liquid crystal display screen image quality.At two fluorescent tubes and the liquid crystal display screen more than two fluorescent tubes, because fluorescent tube is to be lighted by the alternating voltage about 200-1000V/50KHZ, and the CCFL fluorescent tube is installed in the liquid crystal, peripheral parasitic capacitance is arranged between fluorescent tube metallic reflector and the fluorescent tube, therefore exist certain leakage current to cause the lamp current consistency poor, and the consistency of the consistency of lamp luminescence decision liquid crystal display screen brightness.For performance and security requirement, when lamp works is unusual,, need inverter that protective effect is arranged as fluorescent tube open circuit, lamp tube air leaking, joint loose contact, line inverse time, close output voltage.The inverter of technology has only open circuit protecting function now; when inverter only has open circuit protecting function; have only inverter output to possess protection behind the open circuit fully; if but the lamp tube joint loose contact do not protect and contact point discharge can occur and damage liquid crystal display screen, occur easily simultaneously causing potential safety hazard because of the discharge generation naked light.Lamp tube air leaking, working long hours during the anti-or current error of line to cause fluorescent tube aging in advance and reduce brightness.Also there be not simple and practical solution aspect the current error protection at present.

Summary of the invention

The purpose of this utility model provides a kind of current error protection cold-cathode tube-use inverter, and the technical problem that solve is to make the liquid crystal display screen fluorescent tube have defencive function when current error, lamp tube air leaking and loose contact, improves liquid crystal display screen image quality and fail safe.

The utility model is by the following technical solutions: a kind of current error protection cold-cathode tube-use inverter; described current error protection cold-cathode tube-use inverter has control chip U1; the signal of control chip U1 output is through metal-oxide-semiconductor system step-up transformer; drive the cold-cathode fluorescence lamp of liquid crystal display screen; from the signal of cold-cathode fluorescence lamp feedback through feedback circuit to control chip U1; step-up transformer output stage two ends also are connected to current error protection sample circuit, the signal of sampling through protective circuit to control chip U1.

Control chip U1 of the present utility model controls its work by switch.

Control chip U1 of the present utility model adopts DP8600, and it produces pulse width modulating signal and exports from the 9th, 10 pin, through the 5th and the 6th triode (Q5, Q6), the 5th and the 6th diode (D5, D6), to metal-oxide-semiconductor.

Metal-oxide-semiconductor Q3 of the present utility model adopts APM9945,5,6 pin and 7, that 8 pin are connected step-up transformer T1 respectively is elementary.

Step-up transformer T1 of the present utility model adopts EEL19-013aH.

Current error of the present utility model protection sample circuit adopts the secondary output end that is connected in parallel on step-up transformer T1 after the 18 and the 19 capacitor C 18, the C19 series connection, at the intermediate connection point of two series capacitances through the 20 capacitor C 20 ground connection.

The alternating voltage of protective circuit of the present utility model after to the 20 capacitor C 20 dividing potential drops by the 3rd diode D3 rectification after the conducting of control the 7th triode Q7 remove to trigger 15 pin of control chip U1.

Feedback circuit of the present utility model is that the 18 resistance R 18 that is connected with the load cold-cathode tube constitutes.

The the of the present utility model the 18 and the 19 capacitor C 18, C19 adopt 5pF/3Kv, and the 20 capacitor C 20 adopts 1000pF/50V, and the 18 resistance R 18 adopts 2001.

The utility model compared with prior art; adopt common cheaply electric capacity; detecting the drift of transformer mid-point voltage detects as protection; realize CCFL lamp current error protection, open-circuit-protection, the protection of single channel output shorted to earth, single fluorescent tube short-circuit protection and LCC protection simultaneously, safe and reliable, simple in structure.

Description of drawings

Fig. 1 is the circuit block diagram of the utility model embodiment.

Fig. 2 is the circuit theory diagrams of Fig. 1.

Embodiment

Below in conjunction with drawings and Examples the utility model is described in further detail.Current error protection cold-cathode tube-use inverter of the present utility model converts the 12V dc voltage power supply to 1000 volts, the bright cold-cathode fluorescence lamp CCFL of 50KHZ interchange Constant Electric Current pressure point fluorescent tube.As shown in Figure 1; current error protection cold-cathode tube-use inverter of the present utility model; switch control control chip U1 work; the signal controlling metal oxide semiconductor metal-oxide-semiconductor of control chip U1 output turns on and off; turning on and off of metal-oxide-semiconductor makes step-up transformer output High AC voltage; drive the cold-cathode fluorescence lamp of liquid crystal display screen; from the signal of cold-cathode fluorescence lamp feedback through feedback circuit to control chip U1; step-up transformer time utmost point two ends also are connected to current error protection sample circuit, the signal of sampling through protective circuit to control chip U1.

As shown in Figure 2, the first and second triode Q1, Q2 constitutes switch control, control control chip U1 work, switch control chip U1 adopts DP8600, its inner oscillating circuit produces the pulse width modulation (PWM) control signal from the 9th of IC, the output of 10 pin, through external drive the 5th and the 6th triode Q5, Q6, the the 5th and the 6th diode D5, D6, be used to control turning on and off of metal-oxide-semiconductor Q3, metal-oxide-semiconductor Q3 adopts APM9945, its output (the metal-oxide-semiconductor D utmost point) 5,6 pin and 7,8 pin connect step-up transformer T1 elementary 1 respectively, 7 pin, the electric current of control step-up transformer T1 primary coil alternately flows, and at the inner alternating magnetic field that produces of magnetic core of transformer, the transformer secondary output coil produces induced electromotive force, form high pressure at the secondary coil output, step-up transformer T1 adopts EEL19-013aH.High pressure outputs to fluorescent tube Lamp1 and fluorescent tube Lamp2 through the second and the 3rd connector CN2, CN3 with voltage signal.Current balance type detects after capacitor C 18, C19 (5PF/3KV) series connection and at step-up transformer T1 high-voltage output end.In the middle of series capacitance C18 and C19, be connected jumbo the 20 capacitor C 20 (1000PF/50V) to ground, C18 and the detected offset voltage of C19 are carried out dividing potential drop.The conducting of control the 7th triode Q7 is removed to trigger control chip U1 and is produced the protection action behind the ac voltage rectifier of the 3rd diode D3 after to the 20 capacitor C 20 dividing potential drops.

The concrete course of work: when the voltage of transformer output voltage U ab is 1000V.In cycle, electric current holds 1 pin of CN2 to flow to ground again behind fluorescent tube Lamp1 from A at A+/B-(positive half cycle), and electric current again through CN3 flow back into transformer B end through the second diode D2 to Lamp2 from ground wire.(negative half period) electric current was opposite with the positive half cycle flow direction when output current was anti-phase, and unique difference is that negative half-cycle current not only passes through D2, also flow back into the A end by 18 resistance R 18, forms current voltage drop as FEEDBACK CONTROL voltage on R18.Because R18, the D2 pressure drop in circuit is very little, can ignore in the analysis.As fluorescent tube Lamp1, when the Lamp2 parameter is identical with peripheral parasitic capacitance, fluorescent tube Lamp1, the electric current at Lamp2 two ends is equally big, voltage is also identical, the mid point that current balance type detects capacitor C 18, C19 be through C20 to ground, so C18, C19 both end voltage are also identical, also are almost 0V at the mid-point voltage Uc of its series connection.This moment transformer zero potential also at the mid point of transformer secondary output coil.If it is bigger to work as the less or peripheral parasitic capacitance of fluorescent tube Lamp1 internal resistance, at this moment electric current can form leakage current through parasitic capacitance from the fluorescent tube high-pressure side, cause the inconsistent of two fluorescent tube real work electric currents.Because the less or peripheral parasitic capacitance of internal resistance of fluorescent tube Lamp1 is bigger; voltage at fluorescent tube Lamp1 two ends just is lower than the voltage at fluorescent tube Lamp2 two ends; the voltage at capacitor C 18 two ends also is lower than the voltage at C19 two ends; electric capacity mid-point voltage Uc=Ua-Ub; voltage U c is rectified into direct voltage by the 3rd diode D3 again makes the 7th triode Q7 conducting after the 26 and 27 resistance R 26, R27 dividing potential drop through obtaining comparatively safe alternating voltage after the C20 dividing potential drop, and 15 pin of U1 detect after the low level circuit and close output and play a protective role.This circuit mainly detects the consistency of two fluorescent tubes of series loop, so open-circuit-protection, short-circuit protection, and the LCC test all will have influence on the consistency of fluorescent tube to a great extent, so this circuit can play a protective role to the CCFL inverter comprehensively.

The utility model adopts CCFL fluorescent tube tandem-type connection at two fluorescent tubes and the liquid crystal display screen inverter more than two fluorescent tubes, be to be parallel to transformer secondary output high-tension coil two ends again after fluorescent tube and the series connection, the mid point of serially connected lamp tubes connects current sampling resistor over the ground, liquid crystal display screen fluorescent tube parameter error in single group than hour, the voltage and current consistency of fluorescent tube is better.Because what be applied to lamp tube ends is 50KHZ, 1000 volts alternating voltage, in single voltage cycle, two serially connected lamp tubes two ends will occur with respect to mid point (ground connection) generating positive and negative voltage of connecting.If two the fluorescent tube parameters and the parasitic capacitance of series connection are just the same, the voltage of the intermediate point of fluorescent tube series connection is exactly zero to lie prostrate.The same relative ground wire of transformer secondary output high-tension coil mid-point voltage also is zero volt.When lamp tube current error occurs because of the variation of fluorescent tube or peripheral parameter, difference appears in the pressure drop meeting that produces two lamp tube ends, thereby also can cause the drift of transformer mid point, at this moment will can not be zero volt at transformer secondary output high-tension coil mid-point voltage, therefore will embody the error of lamp current parameter at the voltage height of the mid point of serially connected lamp tubes.Because drift in various degree can appear with the error of fluorescent tube in the transformer mid-point voltage, therefore with being connected in parallel on transformer secondary output high-tension coil output again after two low capacity high-voltage capacitance C18, C19 series connection, at this moment the mid point that connects at series capacitance C18, C19 forms dividing potential drop Uc with a large bulk capacitance C20 with being connected to.When lamp current in full accord, the voltage of fluorescent tube too, the transformer mid-point voltage is zero volt, at single alternating voltage capacitor C 18 in the cycle, the mid-point voltage Uc=+Uc18+-Uc19=0V after the C19 dividing potential drop.If difference appears in two lamp currents of series connection; light tube electric voltage also has error simultaneously; drift appears in the mid-point voltage of transformer; in single alternating voltage capacitor C 18 in the cycle; mid-point voltage Uc=+Uc18+-Uc19 after the C19 dividing potential drop no longer is zero volt voltage, and this voltage is used for the protection of inverter as the protection triggering signal behind diode rectification.

Claims

1. a current error is protected the cold-cathode tube-use inverter; it is characterized in that: described current error protection cold-cathode tube-use inverter has control chip (U1); the signal of control chip (U1) output is through metal-oxide-semiconductor system step-up transformer; drive the cold-cathode fluorescence lamp of liquid crystal display screen; from the signal of cold-cathode fluorescence lamp feedback through feedback circuit to control chip (U1); step-up transformer output stage two ends also are connected to current error protection sample circuit, the signal of sampling through protective circuit to control chip (U1).

2. current error protection cold-cathode tube-use inverter according to claim 1, it is characterized in that: described control chip (U1) is controlled its work by switch.

3. current error protection cold-cathode tube-use inverter according to claim 2; it is characterized in that: described control chip (U1) adopts DP8600; it produces pulse width modulating signal from the 9th; the output of 10 pin; through the 5th and the 6th triode (Q5, Q6), the 5th and the 6th diode (D5, D6), to metal-oxide-semiconductor.

4. current error protection cold-cathode tube-use inverter according to claim 3, it is characterized in that: described metal-oxide-semiconductor (Q3) adopts APM9945, and it is elementary that 5,6 pin and 7,8 pin are connected step-up transformer (T1) respectively.

5. current error protection cold-cathode tube-use inverter according to claim 4, it is characterized in that: described step-up transformer (T1) adopts EEL19-013aH.

6. current error protection cold-cathode tube-use inverter according to claim 5; it is characterized in that: described current error protection sample circuit adopts the secondary output end that is connected in parallel on step-up transformer (T1) after the series connection of the 18 and the 19 electric capacity (C18, C19), at the intermediate connection point of two series capacitances through the 20 electric capacity (C20) ground connection.

7. current error according to claim 6 protection cold-cathode tube-use inverter is characterized in that: the conducting that the alternating voltage of described protective circuit after to the 20 electric capacity (C20) dividing potential drop controlled the 7th triode (Q7) after by the 3rd diode (D3) rectification removes to trigger 15 pin of control chip (U1).

8. current error protection cold-cathode tube-use inverter according to claim 7, it is characterized in that: described feedback circuit constitutes for the 18 resistance (R18) that is connected with the load cold-cathode tube.

9. current error protection cold-cathode tube-use inverter according to claim 8; it is characterized in that: the described the 18 and the 19 electric capacity (C18, C19) adopts 5pF/3Kv; the 20 electric capacity (C20) adopts 1000pF/50V, and the 18 resistance (R18) adopts 2001.