Protection apparatus and multi-lamp driving system using the same

A multi-lamp driving system includes a driving apparatus and a current balancer having detection nodes. The protection apparatus includes at least a detection unit and a determining unit. The detection unit includes first impedance devices and a second impedance device. A first end of each first impedance device is coupled with the corresponding detection node. The second impedance device is coupled with a second end of each first impedance device. The cross-voltage between a first end and a second end of the second impedance device is relative to the sum of the voltage level of the detection nodes coupled with the first impedance devices. The determining unit coupled with the second impedance device of the detection unit outputs a protection signal to disable the driving apparatus according to the cross-voltage between the first and second ends of the second impedance device when at least one of the lamps malfunctions.

This application claims the benefit of Taiwan application Serial No. 95219645, filed Nov. 7, 2006, the subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a protection apparatus and a multi-lamp driving system using the same, and more particularly to a protection apparatus with high sensitivity and low cost and a multi-lamp driving system using the same.

2. Description of the Related Art

Recently, there are some patents which disclose multi-lamp driving systems of large-size displays and current balancers thereof for detecting the malfunctioning lamps in order to reduce damage to the components. The disclosed multi-lamp driving system of the large-size display and the current balancer thereof cooperate with a protection circuit to provide better protection.

Please referring toFIG. 1, a conventional multi-lamp driving system is illustrated inFIG. 1. A ring balancer110disclosed in European Patent No. 1,671,521 is applied to the multi-lamp driving system100. A protection circuit120is for malfunction protection (open circuit, short circuit or overload) of lamps. However, the ring balancer110is disposed at a high voltage end of the lamps L1˜Lk. When one or more of the lamps malfunction, the sensitivity of signals transmitted from stray capacitors C11˜Cn2to detection node voltages V1˜Vk is insufficient. The protection circuit120malfunctions easily and is not able to output a protection signal S to control a driving circuit or shut down the power.

In a floating type current balancer disclosed in European Patent No. 1,581,030 or a Zaulas type current balancer disclosed in Japan Patent No. 2004-335443, a detection diode is used in a protection circuit. When one of the lamps malfunctions, a corresponding balance transformer in the current balancer generates extremely high voltage. Therefore, the detection diode has to sustain high voltage and therefore costs more. Furthermore, a large-size display needs a large area light source. In other words, more lamps are needed, and the number of detection diodes is increased accordingly. As a result, the cost is increased as well.

Therefore, it is very important to reduce the cost of the protection circuit and increase the sensitivity of detecting the malfunctioning lamp.

SUMMARY OF THE INVENTION

The invention is directed to a protection apparatus and a multi-lamp driving system using the same. A general impedance device is used in the protection apparatus to replace a high voltage diode. Even when a current balancer is disposed at a high voltage side of the lamps, the protection apparatus still has much higher sensitivity in detecting the malfunctioning lamp. Therefore, the protection apparatus of the present invention decreases the manufacturing cost effectively, and the multi-lamp driving system using the same provides better protection.

According to the present invention, a protection apparatus used in a multi-lamp driving system is provided. The multi-lamp driving system includes a driving apparatus and a current balancer. The driving apparatus is for driving several lamps. The current balancer is for balancing the current flowing through each of the lamps and includes several detection nodes. The protection apparatus includes at least a detection unit and a determining unit. The at least one detection unit includes several first impedance devices and a second impedance device. A first end of each first impedance device is coupled with the corresponding detection node. The second impedance device is coupled with a second end of the first impedance device. The cross-voltage between a first end and a second end of the second impedance device is relative to the sum of the voltage level of the detection nodes coupled with the first impedance devices. The determining unit is coupled with the second impedance device of the at least one detection unit. When determining at least one of the lamps malfunctions according to the cross-voltage between the first end and the second end of the second impedance device, the determining unit outputs a protection signal to disable the driving apparatus.

According to the present invention, a multi-lamp driving system is provided. The multi-lamp driving system includes a driving apparatus, a current balancer and a protection apparatus. The driving apparatus is for driving several lamps. The current balancer is for balancing the current flowing through each of the lamps and includes several detection nodes. The protection apparatus includes at least a detection unit and a determining unit. The at least one detection unit includes several first impedance devices and a second impedance device. A first end of each impedance device is coupled with the corresponding detection node. The second impedance device is coupled with a second end of each impedance device. The cross-voltage between a first end and a second end of the second impedance device is relative to the sum of the voltage level of the detection nodes coupled with the first impedance devices. The determining unit is coupled with the second impedance device of the at least one detection unit. When determining at least one of the lamps malfunctions according to the cross-voltage between the first end and the second end of the second impedance device, the determining unit outputs a protection signal to disable the driving apparatus.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

Please referring toFIG. 2, a block diagram of a multi-lamp driving system according to a first embodiment of the present invention is illustrated inFIG. 2. The multi-lamp driving system200includes a driving apparatus210, a current balancer220, a protection apparatus230and a feedback apparatus240. The driving apparatus210including a PWM control IC, a full bridge module and a high voltage transformer is for driving several lamps L1˜Ln. N is a positive integer. The lamps L1˜Ln are cold cathode fluorescent lamps (CCFL) for example. The current balancer220includes several detection nodes d1˜dk, and k is a positive integer. In the first embodiment, the current balancer220is disposed at a high voltage end of the lamps L1˜Ln as an example.

The protection apparatus230includes at least a detection unit231and a determining unit232. The detection unit231includes several first impedance devices z1˜zk and a second impedance device z. The first impedance device zi is coupled with the corresponding detection node di, and i=1˜k. A first end of the second impedance device z is coupled with second ends of the first impedance devices z1˜zk. In the first embodiment, the current balancer220further includes a reference node d. A second end of the second impedance device is coupled with the reference node d. Though the chosen detection nodes d1˜dk and the reference node d (illustrated as follow), the cross-voltage between the first end and the second end of the second impedance device z is relative to the sum of the voltage level of the detection nodes d1˜dk. Therefore, when at least one of the lamps L1˜Ln malfunctions, the variation of the voltage level of the detection nodes d1˜dk is reflected in the cross-voltage between the two ends of the second impedance device z.

The determining unit232is coupled with the second impedance device z. When determining at least one of the lamps malfunctions according to the cross-voltage between the two ends of the second impedance device z, the determining unit232outputs a protection signal S to disable the driving apparatus210. As a result, the driving signal is not sent to the malfunctioning lamp for protection.

Please referring toFIG. 3A, a first type of the circuit diagram of the multi-lamp driving system inFIG. 2is illustrated inFIG. 3A. InFIG. 3A, the current balancer220is a ring balancer for example. Also, the current balancer220includes several balance transformers221(1)˜221(n). The detection nodes d1˜dk are at one end of a primary side (an output end coupled with the driving apparatus210) of the balance transformers221(1)˜221(n). A common node is at another end of the primary side of the balance transformers221(1)˜221(n) and used as the reference node d. The first impedance devices z1˜zk and the second impedance device z are preferably inductance devices, capacitance devices or resistance devices according to the need. For example, the first impedance devices z1˜zk are capacitance devices and have the same impedance, and the second impedance device z is a resistance device inFIG. 3A.

Moreover, the determining unit232includes a clipper232(1), an isolation circuit232(2), a peak detector232(3) and a comparator232(4). A high voltage side of the isolation circuit232(2) is coupled with the first end and the second end of the second impedance device z through the clipper232(1). Two input ends of the comparator232(4) are coupled with a reference voltage Vref and a low voltage side of the isolation circuit232(2) through the peak detector232(3) respectively.

When the lamps L1˜Ln function normally, the voltage level of the detection nodes d1˜dn is about 10V. When one of the lamps malfunctions, the voltage level of the corresponding detection node reaches 1000V in a very short time. The sensitivity of the cross-voltage variation of the second impedance device z of the present invention is 100 times larger than the conventional one of the protection circuit inFIG. 1. Meanwhile, the isolation circuit232(2) of the determining unit230transforms the input signal from the high voltage side to the low voltage side for a lower-level low voltage circuit. As a result, the lower-level circuit does not interfere with the upper-level circuit. InFIG. 3A, a photo coupler is used as the isolation circuit232(2). However, an isolation transformer can be used as the isolation circuit232(2) in other embodiments. When the isolation circuit232(2) outputs a voltage waveform corresponding to the malfunctioning lamp from the low voltage side, the voltage waveform is transmitted to an input end of the comparator232(4) through the peak detector232(3). Also, when the level is greater than the reference voltage Vref of another input end, the comparator232(4) outputs the protection signal S to disable the driving apparatus210.

As shown inFIG. 3A, the clipper232(1) increases the difference between the cross-voltage of the second impedance device z when the lamps functioning normally and the one when one of the lamps malfunctioning through a zener diode. The peak detector232(3) outputs the maximum level of the received voltage waveform by charging the capacitance through the diode. As a result, the sensitivity of the protection apparatus230is increased. However, the inner circuits of the above components are not limited to the drawings. Moreover, the clipper232(1) can also be disposed at the low voltage side of the isolation circuit232(2).

Please referring toFIG. 3B, a second type of the circuit diagram of the multi-lamp driving system inFIG. 2is illustrated inFIG. 3B. The difference betweenFIG. 3BandFIG. 3Ais that the primary sides of the balance transformers222(1)˜222(n) of the current balancer220are in series connection (as disclosed in Taiwan Patent No. M291174). The detection nodes d1˜dk (similarly k=n) are at one end of the secondary sides of the balance transformers222(1)˜222(n). The common node of another end of the secondary sides of the balance transformers222(1)˜222(n) can be used as the reference node d.

Please referring toFIG. 3C, a third type of the circuit diagram of the multi-lamp driving system inFIG. 2is illustrated inFIG. 3C. The difference betweenFIG. 3CandFIG. 3Bis that an isolation transformer is used in the isolation circuit232(2). Also, the clipper232(1) is coupled between the peak detector232(3) and the comparator232(4).

Please referring toFIG. 3D, a fourth type of the circuit diagram of the multi-lamp driving system inFIG. 2is illustrated inFIG. 3D. The difference betweenFIG. 3DandFIG. 3Cis that the current balancer220is a Zaulas type current balance as an example and includes several balance transformers224(1)˜224(7). Furthermore, the common node of the primary side and the secondary side of the balance transformer224i) is used as the detection node di (i=1˜4). The common node (coupled with the output end of the driving apparatus210) of the primary side and the secondary side of the balance transformer224(7) is used as the reference node d. Moreover, the number of the first impedance devices of the determining unit231is not the same as the number of the lamps.

Second Embodiment

Please referring toFIG. 4, a circuit diagram of a multi-lamp driving system according to a second embodiment of the present invention is illustrated inFIG. 4. The difference between the multi-lamp driving system400inFIG. 4and the multi-lamp driving system inFIG. 3Bis that the protection apparatus430includes two detection units431aand431b. The determining unit432includes two clippers432(1)aand432(1)b, two isolation circuits432(2)aand432(2)band two peak detectors432(3)aand432(3)bcorrespondingly, which are coupled with the same input end of the comparator432(4). Furthermore, the detection nodes d1˜dk (k=n) are divided into two parts, d1˜dm and d(m+1)˜dk. M is a positive integer between 2 and k. As shown inFIG. 4, the detection units431aand431bare respectively coupled with the detection nodes d1˜dm and d(m+1)˜dk. Similar to the first embodiment, when one of the lamps L1˜Lm malfunctions, the determining unit432performs the protection procedure according to the cross-voltage variation of the second impedance device za in the detection unit431a. When one of the lamps L(m+1)˜Ln malfunctions, the determining unit432performs the same protection procedure.

The present embodiment is used when the number of the lamps increases and the sensitivity of the cross-voltage variation of the second impedance device decreases. Therefore, another detection unit is for sharing part of the detection nodes. Of course, the detection nodes d1˜dk can be divided into more parts, and more detection units are used accordingly in order to maintain or increase the sensitivity of the protection apparatus.

Third Embodiment

Please referring toFIG. 5, a circuit diagram of a multi-lamp driving system according to a third embodiment of the present invention is illustrated inFIG. 5. The difference between the multi-lamp driving system500of the present embodiment and the multi-lamp driving system200inFIG. 3Dis that there is no reference node in the present embodiment. The first ends of the first impedance device z1˜z4of the detection unit531are coupled with the detection nodes d1˜d4respectively. The first impedance devices z5and z6are coupled with the detection nodes d5and d6respectively. The second ends of the first impedance devices z1˜z4are coupled with the first end of the second impedance device z. The second ends of the first impedance devices z5and z6are coupled with the second end of the second impedance device z.

However, anyone who has ordinary skill in the field of the present invention can understand that the present invention is not limited to the above embodiments. For example, the protection apparatus of the present invention can be used when the current balancer is disposed at the low voltage end of the lamps (as a floating-type current balancer disclosed in European Patent No. 1,581,030). Furthermore, although the current balancer of the first embodiment includes the reference node, each first impedance device and the second impedance device can still be coupled according the embodiments. Moreover, similar to the second embodiment, the detection units in the third embodiment can be respectively coupled with the detection nodes in order to maintain or increase the sensitivity when the number of the lamp increases. Furthermore, the number and the location of the detection nodes are adjustable according to the type of the current balancer, the coupling method of the shunt and the reference node. When the capacitance is used as the impedance device, the impedance can be formed by the copper foil on a general circuit board for reducing the manufacturing cost.

In the protection apparatus and the multi-lamp driving system using the same according to the above embodiments, a general impedance device is used to replace to the high voltage diode. Even when the current balancer is disposed at the high voltage end of the lamps, the protection apparatus has much higher sensitivity than the conventional one in detecting the malfunctioning lamp. Therefore, the protection apparatus of the present invention decreases the manufacturing cost effectively and provides better protection for the multi-lamp driving system using the same.