Patent Grant
7365502
1. Field of the Invention
The invention relates to electronic driving devices, and particularly to a device for driving a light source such as a discharge lamp of a liquid crystal display (LCD) panel.
2. Related Art
Conventionally, discharge lamps such as cold cathode fluorescent lights (CCFLs) have been used as light sources for liquid crystal display (LCD) panels. Because a plurality of discharge lamps are required for sufficient light intensity in each LCD, high voltages must be added to two ends of each discharge lamp in a large LCD panel. However, impedance differences of the discharge lamps cause unbalanced current flowing through the discharge lamps. The imbalance not only affects luminance uniformity of the LCD panels, but also shortens lifetime of discharge lamps due to large current.
To solve the above problem, a conventional device for driving discharge lamps utilizes a plurality of transformers to balance the current flowing through the discharge lamps.
In the conventional device, the current flowing through the discharge lamps is balanced by the transformers. However, cost of the device is high, and a circuit structure is more complex due to more transformers being used. In addition, a yield rate is lowered when the devices are mass-produced.
An exemplary embodiment of the present invention provides a device for driving a light source including a first lamp and a second lamp. The device includes a first power supply circuit, a second power supply circuit, a first transformer, a second transformer, a first current balancing component and a second current balancing component.
The first transformer and the second transformer are respectively connected to the first power supply circuit and the second power supply circuit, for converting signals respectively received from the first power supply circuit and the second power supply circuit to alternating current (AC) signals. The first current balancing component and the second current balancing component are used for balancing current flowing through the light source, and respectively have two input ends and two output ends.
The two input ends of the first current balancing component are jointly connected to the first transformer, and the two output ends of the first current balancing components are respectively for connection to the first lamp and the second lamp. The two input ends of the second current balancing component are jointly connected to the second transformer, and the two output ends of the second current balancing component are respectively for connection to the first lamp and the second lamp.
The first feedback circuit is connected between the first transformer and the first power supply circuit, for feeding back current flowing through the light source. The second feedback circuit is connected between the second transformer and the second power supply circuit, for also feeding back current flowing through the light source.
Another exemplary embodiment of the present invention provides a larger device for driving a plurality of light sources. The light sources respectively include a first lamp and a second lamp. The device includes a first power supply circuit, a second power supply circuit, a first transformer, a second transformer, a plurality of first current balancing components and a plurality of second current balancing components, a first feedback circuit and a second feedback circuit. A number of the light sources, the first current balancing components and the second current components is respectively defined as n, where n is an integer from 1 to (k+1). Each of the first current balancing components and the second current balancing components has two input ends and two output ends.
The first transformer and the second transformer are respectively connected to the first power supply circuit and the second power supply circuit, for converting signals respectively received from the first power supply circuit and the second power supply circuit to AC signals. The first current balancing components and the second current balancing components are used for balancing current flowing through the light sources.
The two input ends of the first current balancing components are jointly connected to the first transformer, and the two output ends of the kth first current balancing components are respectively for connection to the first lamp and the second lamp of the kth light source. The two input ends of the second current balancing components are jointly connected to the first transformer, and the two output ends of the kth second current balancing components are respectively for connection to the second lamp in the kth light source and the first lamp in the (k+1)th light source, and the two output ends of the (k+1)th second current balancing component are respectively for connection to the second lamp in the kth light source and the first lamp in the first light source.
The first feedback circuit is connected between the first transformer and the first power supply circuit, for feeding back current flowing through the light sources. The second feedback circuit is connected between the second transformer and the second power supply circuit, for also feeding back current flowing through the light sources.
Another exemplary embodiment of the present invention provides a larger device for driving a plurality of light sources. The device includes a power supply circuit, a second power supply circuit, a first transformer, a second transformer, a plurality of first current balancing components and a plurality of second current balancing components, a first feedback circuit and a second feedback circuit. A number of the light source, the first current balancing components and the second current balancing components is respectively defined as n, where n is an integer from 1 to (k+1). Each of the first current balancing components and the second current balancing components has two input ends and two output ends. The first light source to the kth light source respectively includes a first lamp and a second lamp, and the (k+1)th light source includes only a lamp.
The first transformer and the second transformer are respectively connected to the first power supply circuit and the second power supply circuit, for converting signals respectively received from the first power supply circuit and the second power supply circuit to AC signals. The first current balancing components and the second current balancing component are used for balancing current flowing through the light sources.
The two input ends of the first current balancing components are jointly connected to the first transformer, and the two output ends of the kth first current balancing component are respectively connected to the first lamp and the second lamp of the kth light source, and the lamp of the (k+1)th light source is connected to the end of the secondary winding of the first transformer. The two input ends of the second current balancing components are jointly connected to the second transformer, and the two output ends of the kth second current balancing component are for respectively connection to the second lamp of the kth light source and the lamp of the (k+1)th light source, and the first lamp of the first light source is connected to the second transformer.
The first feedback circuit is connected between the first transformer and the first power supply circuit, for feeding back current flowing through the light sources. The second feedback circuit is connected between the second transformer and the second power supply circuit, for also feeding back current flowing through the light sources.
Other advantages and novel features will be drawn from the following detailed description of preferred embodiments of the present invention with the attached drawings, in which:
In the exemplary embodiment, the device is divided into a left part and a right part with the light source L11 disposed therebetween. Components of the left part and the right part are the same, so only the left part of the device is described hereinafter.
The DC/AC converter 11 converts DC signals received from the DC power source 10 to AC signals. The transformer 12, connected to the DC/AC converter 11, converts the AC signals to another AC signals transmitted to the light source L11 via the current balancing components 13. In the exemplary embodiment, the AC signals output from the DC/AC converter 11 are square wave signals, and the AC signals output from the transformer 12 are sine wave signals. The current balancing component 13 is used for balancing current flowing through the lamps a1 and a2. The feedback circuit 14 is connected between the transformer 12 and the DC/AC converter 11 for feeding back total current flowing through the lamps a1 and a2 to the DC/AC converter 11. In the exemplary embodiment, the feedback circuit 14 includes a dual diode circuit.
In alternative exemplary embodiments, the feedback circuit 14 can be other circuits. Signals output from the DC/AC converter 11 are varied according to the signals output from the feedback circuit 14, directly affecting brightness of the lamps a1 and a2.
In the exemplary embodiment, the DC/AC converter 11 may be a full bridge circuit, a half bridge circuit, a push-pull circuit, or a Royer circuit.
In the exemplary embodiment, phases of the AC signals respectively output from the transformers 12 and 12′ are opposite. That is, the AC signals output from the transformer 12′ are negative while the AC signals output from the transformer 12 are positive, and vice versa. Therefore, the current flowing through the lamps a1 and a2 is two times as much as the current generated only by the left part or the right part.
In alternative exemplary embodiments, the device can include only one DC power source, either 10 or 10′, supplying DC power to both the left part and the right part.
In the exemplary embodiment, the current balancing component 13 comprises a first winding W1 and a second winding W2. Two input ends of the current balancing component 13 are at a side of the first winding W1 and a second winding W2, and two output ends of the current balancing component 13 are at another side of the first winding W1 and a second winding W2. The input ends of the current balancing component 13 are jointly connected to the transformer 12, and the output ends of the current balancing component 13 are respectively connected to the lamp a1 and lamp a2. A number of turns N1 of the first winding W1 and a number of turns N2 of the second winding W2 are the same. Inductance L1 of the first winding W1 and inductance L2 of the second winding W2 are substantially equal in magnitude. The current flowing through the first winding W1 is defined as I1, and the current flowing through the second winding W2 is defined as I2. The current I1 and I2 are equal in magnitude because the N1 is equal to the N2. Based on Lenz's law, mutual inductance between the first winding W1 and the second winding W2 is M12 and M21. The M12 and the M21 are equal in magnitude, and both of them are equal to the L1 and L2. An impedance of the lamp a1 is defined as R1, and an impedance of the lamp a2 is defined as R2. If the R1 is not equal to the R2, basic equations of voltages in accordance with the transformer 12 are as follows:
V=(sL1+R1)*I1−sM12I2 (1)
V=(sL2+R2)*I2−sM21I1 (2)
In the exemplary embodiment, the V is value of voltages output from the transformer 12. Then, a following equation is obtained from equations (1) and (2)
(2*sL1+R1)*I2=(2*sL2+R2)*I1 (3)
An inequality of (2*sL1=2*sL2)>>(R1 and R2) is obtained from equation (3). That is, both of 2*sL1 and 2*sL2 are greater than the largest value of the R1 and the R2. In the exemplary embodiment, value of the s is (2π f), in which f is a frequency of the current flowing through the lamps a1 and lamp a2.
In the exemplary embodiment, the DC/AC converters 31 and 31′ may be a full-bridge circuit, a half-bridge circuit, a push-pull circuit, or a Royer circuit.
In the exemplary embodiment, connections between the light sources L3n (n=1, 2, 3, . . . , n) and the current balancing components CC3n′ (n=1, 2, 3, . . . , n) are different from those of the light sources L3n (n=1, 2, 3, . . . , n) and the current balancing components CC3n (n=1, 2, 3, . . . , n). The device is divided into a left part and a right part with the light source L3n (n=1, 2, 3, . . . , n) disposed therebetween. In the left part, the input ends of the current balancing components CC3n (n=1, 2, 3, . . . , n) are jointly connected to the transformer 32, and the output ends of the current balancing components CC3n (n=1, 2, 3, . . . , n) are respectively connected to a first lamp a1 and a second lamp a2 of a corresponding light source L3n (n=1, 2, 3, . . . , n). That is, a first winding W1 and a second winding W2 of a current balancing component CC31 are respectively connected to a first lamp a1 and a second lamp a2 of a light source L31, a first winding W1 and a second winding W2 of a current balancing component CC32 are respectively connected to a first lamp a1 and a second lamp a2 of a light source L32, and so on through to a first winding W1 and a second winding W2 of a current balancing component CC3n are respectively connected to a first lamp a1 and a second lamp a2 of a light source L3n. Therefore, the current balancing component CC31, balances current flowing through the two lamps in the light source L31, the current balancing component CC32 balances current flowing through the two lamps in the light source L32, and so on through to the current balancing component CC3n balances current flowing through the two lamps in the light source L3n.
In the right part, the input ends of the current balancing components CC3n′ (n=1, 2, 3, . . . , n) are also jointly connected to the transformer 32′. However, a first winding W1′ and a second winding W2′ of a current balancing component CC31′ are respectively connected to the lamp a2 of the light source L31 and the lamp a1 of the light source L32, a first winding W1′ and a second winding W2′ of a current balancing component CC32′ are respectively connected to the lamp a2 of the light source L32 and a lamp a1 of the light source L33, and so on through to a first winding W1′ and a second winding W2′ of a current balancing component CC3n′ are respectively connected to the lamp a2 of the light source L3n and the lamp a1 of the light source L31. Therefore, the current balancing component CC31′ balances current flowing through the lamp a2 of the light source L31 and the lamp a1 of the light source L32, the current balancing component CC32′ balances current flowing through the lamp a2 of the light source L32 and the lamp a1 of the light source L33, and so on through to the current balancing component CC3n′ balances current flowing through the lamp a2 of the light source L3n and the lamp a1 of the light source L31.
In conclusion, the current balancing components CC3n and CC3n′ (n=1, 2, 3, . . . , n) balances the current flowing through each lamp of the light sources L3n (n=1, 2, 3, . . . , n).
Similarly, in the exemplary embodiment, phases of the AC signals output from the transformers 32 and 32′ are opposite. Therefore, current flowing through the lamps a1 and a2 is two times as much as the current generated only by the left part or the right part.
In the left part, the input ends of the current balancing components CC4n (n=1, 2, 3, . . . , n) are jointly connected to the transformer 42, and the output ends of the current balancing components CC4n (n=1, 2, 3, . . . , n) are respectively connected to a corresponding light source L4n (n=1, 2, 3, . . . , n). That is, the first winding W1 and a second winding W2 of the current balancing component CC41 are respectively connected to the lamp a1 and the lamp a2 of the light source L41, the first winding W1 and the second winding W2 of the current balancing component CC42 are respectively connected to the lamp a1 and the lamp a2 of the light source L42, and so on through to the first winding W1 and a second winding W2 of the current balancing component CC4n are respectively connected to the lamp a1 and the lamp a2 of the light source L4n. In addition, the lamp a′ of the light source L4(n+1) is directly connected to the first transformer 42. Therefore, the current balancing components CC4n (n=1, 2, 3, . . . , n) balances the currents flowing through the lamp a1 and the lamp a2 of each light source.
In the right part, the input ends of the current balancing components CC4n′ (n=1, 2, 3, . . . , n) are also jointly connected to the transformer 42′. However, the first winding W1′ and a second winding W2′ of the current balancing component CC41′ are respectively connected to the lamp a2 of the light source L41 and lamp a1 of the light source L42, the first winding W1′ and the second winding W2′ of the current balancing component CC42′ are respectively connected to the lamp a2 of the light source L42 and the lamp a1 of the light source L43, and so on through to the first winding W1′ and the second winding W2′ of the current balancing component CC4n′ are respectively connected to the lamp a2 of the light source L4n and the lamp a′ of the light source L4(n+1). In addition, the lamp a1 of the light source L41 is directly connected to the first transformer 32′. Therefore, the current balancing components CC4n′ (n=1, 2, 3, . . . , n) balance the currents flowing through the lamp a2 of one light source and the lamp a1 of another light source.
In conclusion, the current balancing components CC4n and CC4n′ (n=1, 2, 3, . . . , n) balance the currents flowing through each lamp of the light sources.
Similarly, in the exemplary embodiment, phases of the AC signals output from the transformers 42 and 42′ are opposite. Therefore, current flowing through the lamps a1 and a2 is two times as much as the current generated only by the left part or the right part.
Thus, the invention minimizes the number of transformers such that assembly and material costs can be greatly reduced and the circuitry structure is simplified while current flowing through the light sources is balanced.
While particular embodiments of the invention have been described above, it should be understood that it has been presented by way of examples only and not by way of limitation. Thus the breadth and scope of the invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005 1 0035550 | Jun 2005 | CN | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6420839 | Chiang et al. | Jul 2002 | B1 |
| 6534934 | Lin et al. | Mar 2003 | B1 |
| 6781325 | Lee | Aug 2004 | B2 |
| Number | Date | Country | |
|---|---|---|---|
| 20060290297 A1 | Dec 2006 | US |
