[background technology]
At present, the panel of LCD (LCD) mainly adopts discharge lamp (Discharge Lamp) as backlight, and this kind discharge lamp needs higher driving voltage just can light.In order to ensure the operate as normal of discharge lamp, and make electric current maintain steady state value, need the electric current of feedback circuit feedback flow usually, judge the operating state of discharge lamp with this through discharge lamp by it.
Figure 1 shows that existing discharge lamp driven apparatus, this existing discharge lamp driven apparatus comprises power-switching circuit 11, transformation resonance circuit 12, resonant circuit 13, feedback circuit 14, PWM controller 15 and discharge lamp L1.
Wherein, transformation resonance circuit 12 comprises transformer T1 and capacitor C 11, and capacitor C 11 is connected between transformer T1 secondary winding high-pressure side and the ground, and the leakage inductance of itself and transformer T1 can play the effect of resonance.Resonant circuit 13 comprises inductance L 11 and resonant capacitance C12 and C13.Wherein, resonant capacitance C12 and C13 are connected in series between transformer T1 secondary winding high-pressure side and ground, and inductance L 11 is connected between transformer T1 secondary winding high-pressure side and the resonant capacitance C12.
In discharge lamp driven apparatus, each several part circuit and LCD panel enclosure all can produce stray electrical current (stray current) between (can regard as with reference to ground), thereby make the electric current that not only comprises the discharge lamp L1 that flows through in the current feedback signal, the stray electrical current that also comprises whole circuit and produced.So, in the whole discharge lamp driven apparatus, capacitor C 11, the stray electrical current that C12 and C13 produced are bigger, thereby it is bigger for the current feedback signal error effect.
[summary of the invention]
In view of this, need provide a kind of discharge lamp driven apparatus, reduce the influence of stray electrical current, improve the accuracy of current feedback signal the discharge lamp current feedback signal.
A kind of discharge lamp driven apparatus is used to drive discharge lamp, comprises power-switching circuit, transformation resonance circuit, PWM controller and at least one resonant circuit.The conversion of signals that power-switching circuit is used for receiving is an AC signal.Transformation resonance circuit this AC signal that is used to boost, it comprises transformer and electric capacity.Transformer has elementary winding and secondary winding, and electric capacity is connected between this transformer secondary output winding high-pressure side and the low-pressure end.The PWM controller is connected in power-switching circuit, is used to control the size of power-switching circuit output AC signal.Resonant circuit is connected between transformer secondary output winding high-pressure side and the low-pressure end, is used for the AC signal after boosting is converted to the AC signal that can drive discharge lamp.Each resonant circuit comprises inductance and resonant capacitance.Wherein, inductance is connected between transformer secondary output winding high-pressure side and the discharge lamp.Resonant capacitance is connected between discharge lamp and the transformer secondary output winding low-pressure end.Described resonant capacitance is an embedded capacitance.
In the transformation resonance circuit of the present invention, electric capacity is connected between transformer secondary output winding high-pressure side and the low-pressure end, reduces the stray electrical current that produces between transformation resonance circuit and the LCD panel housing, makes the discharge lamp current feedback signal comparatively accurate.
[embodiment]
Fig. 2 is the discharge lamp driven apparatus of an embodiment of the present invention, and this discharge lamp driven apparatus comprises power-switching circuit 21, transformation resonance circuit 22, resonant circuit 23, feedback circuit 24, PWM controller 25 and discharge lamp L2.
The conversion of signals that power-switching circuit 21 is used for receiving is an AC signal, and this AC signal is a square-wave signal.
Transformation resonance circuit 22 links to each other with power-switching circuit 21, this AC signal that is used to boost, and it comprises transformer T2 and capacitor C 21.Transformer T2 has elementary winding and secondary winding, and capacitor C 21 is connected between transformer T2 secondary winding high-pressure side and the low-pressure end, and the leakage inductance of itself and transformer T2 can play the effect of resonance.
Resonant circuit 23 links to each other with transformation resonance circuit 22, promptly is connected between transformer T2 secondary winding high-pressure side and the low-pressure end, is used for the AC signal after boosting is converted to the AC signal that can drive discharge lamp L2.In the present embodiment, the AC signal that can drive discharge lamp L2 is a string ripple signal.
Resonant circuit 23 comprises inductance L 21 and resonant capacitance C22, and wherein, inductance L 21 is electrically connected between transformer T2 secondary winding high-pressure side and the discharge lamp L2, and resonant capacitance C22 is electrically connected between discharge lamp L2 and the transformer T2 secondary winding low-pressure end.In the present embodiment, resonant capacitance C22 is an embedded capacitance, i.e. formed electric capacity between the Copper Foil of circuit board different layers.
In the present embodiment, resonant circuit 23 also comprises resonant capacitance C23, and it is electrically connected between resonant capacitance C22 and the transformer T2 secondary winding low-pressure end.
Feedback circuit 24 links to each other with transformation resonance circuit 22, is used for the electric current of feedback flow through discharge lamp L2, and it comprises filter circuit.Described filter circuit comprises filter capacitor C25, and it is connected between transformer T2 secondary winding low-pressure end and the ground, is used for the noise of filtering discharge lamp current feedback signal.
In the present embodiment, feedback circuit 24 comprises another filter circuit, and it comprises filter capacitor C24 and resistance R 22.Wherein, filter capacitor C24 and resistance R 22 are connected in series, and are connected between transformer T1 secondary winding low-pressure end and the ground, are used for the noise of filtering discharge lamp L2 current feedback signal equally.In the present embodiment, described filter circuit is used for the noise of filtering different frequency, makes that discharge lamp L2 current feedback signal is more accurate.
Feedback circuit 24 comprises resistance R 21 and diode D21, D22.Wherein, the plus earth of diode D22, its negative electrode links to each other with the low-pressure end of transformer T1 secondary winding.The anode of diode D21 links to each other with the negative electrode of diode D22, and resistance R 21 is connected between the negative electrode and ground of diode D21, is used for the current signal of discharge lamp L2 is converted to voltage signal.
PWM controller 25 is connected between feedback circuit 24 and the power-switching circuit 21, promptly is connected between the negative electrode and power-switching circuit 21 of diode D21, is used for the size according to the AC signal of discharge lamp current feedback signal control power-switching circuit 21 outputs.
Consult the discharge lamp driven apparatus of Fig. 3 for another execution mode of the present invention, this discharge lamp driven apparatus and discharge lamp driven apparatus shown in Figure 2 are roughly the same, and difference is: discharge lamp driven apparatus is used to drive discharge lamp L3n (n=1,2,3, ..., n), it comprises resonant circuit 33n (n=1,2,3 ..., n).Wherein, resonant circuit 33n (n=1,2,3 ..., n) link to each other with transformation resonance circuit 32 respectively, and transformation resonance circuit 32, resonant circuit 33n (n=1,2,3 ..., n) identical with the internal structure of transformation resonance circuit 22, resonant circuit 23 among Fig. 2, and transformation resonance circuit 22 is all identical with the annexation of resonant circuit 23 among its two annexation and Fig. 2, therefore, does not repeat them here.In the present embodiment, resonant circuit 33n (n=1,2,3 ..., n) connect respectively corresponding discharge lamp L3n (n=1,2,3 ..., n), with the AC signal behind the resonance export to discharge lamp L3n (n=1,2,3 ..., n).
In the discharge lamp driven apparatus of the present invention, the electric capacity that plays resonance effect in transformation resonance circuit and the resonant circuit all is directly connected between transformer secondary output winding high-pressure side and the low-pressure end, make can not produce stray electrical current between transformation resonance circuit, resonant circuit and the LCD panel housing, and then make the discharge lamp current feedback signal comparatively accurate.