CN201248186Y - Multi-lamp tube current equalizing circuit of display - Google Patents

Abstract

The utility model discloses a multi-lamp tube current-sharing circuit of a display, which is supplied with an alternating current power supply by a lamp tube driving module and comprises a transformer set, a lamp tube set and a current-sharing circuit; the transformer group comprises a first transformer and a second transformer, wherein the primary side of the first transformer and the secondary side of the second transformer are respectively electrically connected with the lamp tube driving module; the lamp tube group comprises a first lamp tube and a second lamp tube which are respectively connected in series with a secondary side dotting end and a non-dotting end of the first transformer, and a third lamp tube and a fourth lamp tube which are respectively connected in series with a secondary side dotting end and a non-dotting end of the second transformer; the current equalizing circuit comprises a first current mirror and a second current mirror, and equalized currents are provided for each lamp tube in a bias current mode through the first current mirror and the second current mirror, so that the picture brightness of the display is uniform.

Description

Display multi-lamp current sharing circuit

technical field

The utility model relates to a multi-lamp current equalizing circuit, in particular to a multi-lamp current equalizing circuit of a display.

Background technique

A cold cathode fluorescent lamp (CCFL for short) is a slender, sealed glass tube filled with an inert gas. When a high voltage is applied to the lamp, the gas is ionized, producing ultraviolet light. However, these features necessitated some special design fits. For example, in order to maximize the lifetime of the lamp, it is necessary to drive the CCFL with an AC waveform. Any direct current component will cause a part of the gas to collect at one end of the tube, causing an irreversible light gradient and causing uneven brightness at both ends of the tube. In addition, in order to improve the efficiency of CCFL, it is necessary to drive the lamp tube with a nearly sinusoidal waveform. Therefore, CCFLs usually require a DC-AC converter to convert the DC supply voltage into an AC waveform of 40kHz to 80kHz.

CCFLs have been used for many years in notebook computers, digital cameras, cell phones, and other devices with small LCD screens. These types of devices usually use only one CCFL. With the emergence of large-size LCD panels, there is a demand for multiple CCFLs. Depending on the size of the LCD panel, the number of CCFLs used may be as many as 30 or even 40. In addition to the CCFL lamps in the LCD display, they must be equally spaced In addition to being evenly distributed across the LCD backplane to provide optimal light distribution, it is most important that all lamps must have the same brightness. For this reason, there is a method in the past, as shown in FIG. 1, is to use a single-channel CCFL controller 91 to drive multiple CCFLs 92. In this way, the CCFL controller 91 monitors the current flowing through the lamp tube only through one of the lamp tubes 92', and simultaneously drives all the parallel-connected lamp tubes 92 with almost the same AC waveform.

However, the above method uses the same waveform to drive all the lamp tubes 92, but due to the difference in the impedance of the lamp tubes 92, the brightness will be uneven, and the brightness of the CCFL will change with the temperature, so it is difficult to keep the brightness of all the lamp tubes consistent. Therefore, it is easy to make the display have obvious bright and dark areas.

Utility model content

The purpose of the utility model is to provide a multi-lamp current equalizing circuit of a display which can maintain uniform brightness of the backlight board of the display.

The multi-lamp current equalizing circuit of the utility model display is supplied with AC power by a lamp driving module, and the multi-lamp current equalizing circuit includes a transformer group, a lamp tube group and a current equalizing circuit; The first transformer and the second transformer electrically connected to the tube driving module; The third lamp tube and the fourth lamp tube on the secondary side of the secondary side of the dotted end and the non-dotted end; the current sharing circuit includes a first current mirror and a second current mirror, and the first current mirror has a first reference end and at least a first output terminal, the first reference terminal is connected in series with the second lamp tube, the first output terminal is connected in series with the fourth lamp tube, the second current mirror has a second reference terminal and at least one second output terminal, The second reference terminal is connected in series with the third lamp tube, and the second output terminal is connected in series with the first lamp tube.

The beneficial effect of the utility model is that the first and second current mirrors provide equalized current to each lamp tube in a biased current manner, thereby making the brightness of the screen of the display more uniform.

Description of drawings

Fig. 1 is a system block diagram illustrating a conventional circuit block for solving uneven brightness of CCFL lamps;

Fig. 2 is a circuit diagram illustrating the first preferred embodiment of the multi-lamp current equalizing circuit of the display of the present invention;

Fig. 3 is a circuit diagram illustrating the second preferred embodiment of the multi-lamp current equalizing circuit of the display of the present invention; and

FIG. 4 is a circuit diagram illustrating a first current mirror circuit of the third preferred embodiment of the multi-lamp current sharing circuit of the display of the present invention.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the utility model is described in detail:

Before describing the present utility model in detail, it should be noted that in the following description, similar elements in different embodiments are denoted by the same numerals.

Referring to Fig. 2, in the first preferred embodiment of the multi-lamp current equalizing circuit of the display of the present invention, an AC power supply is supplied by a lamp drive module 8, and this lamp drive module 8 can be cut by any DC power supply to a high High-frequency pulse and converted into high-frequency sine wave drive circuit with power supply, such as Royer drive circuit, half-bridge drive circuit, full-bridge drive circuit or push-pull drive circuit, etc., which should be well known to those skilled in the art , which will not be repeated here.

The multi-lamp current equalizing circuit includes a transformer group 1, a lamp group 2 and a current equalizing circuit 3; the transformer group 1 includes a first transformer 11 and a second transformer 12, and its primary sides 111, 121 are respectively connected to The lamp drive module 8 is electrically connected; the sine wave current from the lamp drive module 8 is input to the primary sides 111, 121 of the first transformer 11 and the second transformer 12, and after being converted into an appropriate voltage, the sine wave current is then transmitted by the secondary side 112, 122 Output sine wave current; the secondary side 112 of the first transformer 113 has a dotted end 113 and a non-dotted end 114, and the second transformer 122 also has a dotted end 123 and a non-dotted end 124, and the dotted end 113, 123 The output sine wave current is in phase, and the current output by the non-dotted terminals 114, 124 is also in phase, but the currents of the dotted terminals 113, 123 and the non-dotted terminals 114, 124 are opposite phase currents.

The lamp group 2 includes a first lamp tube 21 connected in series to the lighting end 113 of the secondary side 112 of the first transformer 11, a second lamp tube 22 connected in series to the non-starting end 114, and a second lamp tube 22 connected in series to the second transformer 12. A third light tube 23 at the lit end 123 of the secondary side 122 and a fourth light tube 24 at the non-dotted end 124 . It is worth noting that the light tube mentioned in this embodiment generally refers to the cold cathode fluorescent lamp (CCFL) used for the backlight of a general thin display (such as a liquid crystal screen, a plasma display screen), which is well known to those skilled in the art , which will not be repeated here.

The current equalizing circuit 3 includes a first current mirror 31 and a second current mirror 32 having the same circuit structure, and both the first current mirror 31 and the second current mirror 32 are based on two bipolar junction transistors ( The binary junction transistor, hereinafter referred to as BJT) is formed after being electrically connected to each other. Of course, the current mirror can have other types of structures. This embodiment first cites a standard current mirror composed of two BJTs, and the rest of the current mirror structure will be in other Describe in the embodiment again.

The first current mirror 31 has a BJT 301 and a BJT 302; the collector of the BJT 301 is electrically connected to the second lamp tube 22 and is defined as a first reference terminal 311, the bases of the BJT 301 and the BJT 302 are electrically connected to each other, and There is a contact 313, the first reference terminal 311 and the contact 313 are electrically connected to each other, the collector of the BJT 302 is electrically connected to the fourth light tube 24 and defined as a first output terminal 312. The sine wave current output from the non-dotted terminal 114 of the first transformer 11 flows to the first reference terminal 311 through the second lamp tube 22, and the sine wave current output from the non-dotted terminal 124 of the second transformer 12 passes through the fourth lamp tube 24 flows to the first output terminal 312, the two same-phase currents can make the BJT301 and BJT302 in the first current mirror 31 be in the working area at the same time, and based on the working characteristics of the current mirror circuit, the two sinusoidal currents are equalized into almost same amplitude.

As shown in Figure 2, the second current mirror 32 also has a second reference terminal 321 and a second output terminal 322; the sinusoidal current output from the dot terminal 123 of the second transformer 23 flows through the third lamp tube 23 to The second reference terminal 321 , and the sinusoidal current output from the switching terminal 113 of the first transformer 12 flows to the second output terminal 322 through the first lamp tube 21 . Same as the first current mirror 31, the second current mirror 32 can also equalize the two sinusoidal currents into almost the same amplitude, therefore, the current equalizing circuit 3 can pass through the first, second, third and fourth lamps The currents of the tubes 21, 22, 23, and 24 are equalized so that their brightness tends to be consistent.

Referring to FIG. 3 , it shows the second preferred embodiment of the multi-lamp current equalizing circuit of the display of the present invention, wherein most of the components and their connections are the same as those of the first preferred embodiment, and will not be repeated here.

The difference from the first embodiment is that the transformer set 1 of this embodiment further includes a third transformer 13, the primary side 131 of the third transformer 13 is also electrically connected to the lamp driving module 8, and the secondary A dotted terminal 133 and a non-dotted terminal 134 of the side 132 output mutually antiphase sine wave currents. Therefore, the sinusoidal currents flowing through the dotted ends 113, 123, 133 of all the transformers 11, 12, 13 of the transformer group 1 are in phase, and the sinusoidal currents flowing through the non-dotted ends 114, 124, 134 are also in phase.

In this embodiment, the lamp tube group 2 further includes a fifth lamp tube 25 connected in series with the dotting end 133 of the secondary side 132 of the third transformer 13, and a fifth lamp tube 25 connected in series with the non-dotted end 134 of the secondary side 132 of the third transformer 13. Six lamp tubes 26; the first current mirror 31 of the current equalizing circuit 3 also includes a BJT303, the collector of the BJT303 is connected to the sixth lamp tube 26 and is defined as another first output terminal 314, due to the first current mirror 31 The function will make the sinusoidal current output from the non-dotted terminal 134 and pass through the sixth lamp tube 26 and the first output terminal 314 tend to be the same as the current flowing through the first reference terminal 311 and the other first output terminal 312, and then Make the brightness of the second, fourth, and sixth lamp tubes 22, 24, and 26 tend to be consistent. Similarly, the second current mirror 32 can also make the sinusoidal current output from the dotting terminal 133 and pass through the fifth lamp tube 25 and the second output terminal 324 flow through the second reference terminal 321 and another second output terminal 322 The current tends to be the same, so that the brightness of the second, fourth, and sixth lamp tubes 22, 24, and 26 tends to be the same. It is worth noting that the dotted end 133 and the non-dotted end 134 are both located at the two ends of the secondary side 132 of the third transformer 13, so although the current is in anti-phase, the amplitude is consistent with each other, so that the fifth lamp tube 25 The brightness of the sixth lamp tube 26 is equal to that of the first and third lamp tubes 21 and 23 and the second and fourth lamp tubes 22 and 24 .

In fact, the multi-lamp current equalizing circuit of the display of the present invention can also be applied to the solution of more lamps, as long as the newly added transformer 5 is connected to the lamp drive module 8 in the above-mentioned manner, and then the two terminals on the secondary side of the transformer Connect a light tube in series at each end, and connect the light tubes in series with the collectors of the newly added BJTs in the first current mirror 31 and the second current mirror 31, as in the second embodiment, only need to pay attention to the current flowing through the same current mirror The current of all BJTs must be in the same phase, so that the effect of adding lamps and still making each lamp uniform in brightness can be achieved.

In the above embodiment, although both the first current mirror 31 and the second current mirror 32 are standard BJT current mirrors, in fact, other BJT current mirrors with better current sharing effect can be used instead, such as improved Type current mirror (base-current compensation) and Wilson current mirror (Wilson current mirror), or according to actual needs, the BJT current mirror can be replaced by a junction field effect transistor (JFET) current mirror or a metal oxide semiconductor field An effective transistor (MOSFET) can achieve the effect of making the current equalization, or make the current equalization effect better.

Fig. 4 shows the first current mirror 31' of the third preferred embodiment of the multi-lamp current sharing circuit of the display of the present invention. The difference between this embodiment and the previous embodiment is that the first current mirror 31' adopts an Type current mirror structure, a BJT304 is also connected between the contact point 313 and the first reference point 311, the emitter of the BJT304 is electrically connected to the contact point 313, and its collector and base are electrically connected to the first reference terminal 311. The method can reduce the influence of the β value of the BJT on the current sharing effect.

To sum up, the brightness of the CCFL lamp tube is proportional to the current, and the first and second current mirrors 31, 32 are used to drive the CCFL lamp tubes connected to it in a bias current manner to provide equalized current to each Lamp tube, thus making the screen brightness of the display more uniform.

Claims (5)

1. A multi-lamp current equalizing circuit for a display, which is supplied with AC power by a lamp driving module, and the multi-lamp current equalizing circuit includes: a transformer set, including a first transformer and a second transformer, the primary sides of the first transformer and the second transformer are respectively electrically connected to the lamp driving module; and The lamp tube group includes a first lamp tube and a second lamp tube respectively connected in series with the secondary-side activated terminal and a non-discharged terminal of the first transformer, and a first lamp tube respectively connected in series with the secondary-side activated terminal and non-discharged terminal of the second transformer. The third lamp and the fourth lamp; It is characterized in that the multi-lamp current sharing circuit further includes a current sharing circuit, the current sharing circuit includes a first current mirror and a second current mirror, the first current mirror has a first reference terminal and at least one first output terminal, The first reference terminal is connected in series with the second lamp tube, the first output terminal is connected in series with the fourth lamp tube, the second current mirror has a second reference terminal and at least one second output terminal, and the second reference terminal is connected to the fourth lamp tube in series. The third lamp tube is connected in series, and the second output terminal is connected in series with the first lamp tube. 2. The multi-lamp current equalizing circuit of a display according to claim 1, wherein the transformer group further comprises a third transformer, the primary side of the third transformer is electrically connected to the lamp drive module, and the lamp The tube group also includes a fifth lamp tube and a sixth lamp tube respectively connected in series with the secondary side of the third transformer. The first current mirror and the second current mirror respectively include two first output terminals and two The second output terminal, the first output terminal of the first current mirror is respectively connected in series with the fourth lamp and the sixth lamp, and the second output terminal of the second current mirror is connected in series with the first lamp with that fifth light tube. 3. The multi-lamp current equalizing circuit of a display according to claim 1, wherein the circuit of the first current mirror is the same as that of the second current mirror, and the first current mirror includes two bipolar junctions The collectors of the transistor are respectively the first reference terminal and the first output terminal, and the base is electrically connected to a contact point and is electrically connected to the first reference terminal. 4. The multi-lamp current equalizing circuit of a display according to claim 1, wherein the circuit of the first current mirror is the same as that of the second current mirror, and the first current mirror includes three bipolar junctions The collectors of the transistor are respectively the first reference terminal and the first output terminal, and the base is electrically connected to a contact point and is electrically connected to the first reference terminal. 5. The multi-lamp current sharing circuit of the display as claimed in claim 1, wherein the first current mirror also has a bipolar junction transistor, and the base and the collector of the bipolar junction transistor are both It is electrically connected with the first reference terminal, and its emitter is electrically connected with the contact, so as to reduce the influence of the β value of the bipolar junction transistor on the current sharing effect.

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