LED device with simultaneous open and short detection function and method thereof

An LED device with simultaneous open and short detection function includes a plurality of LED strings, a voltage converter, a current driving unit, a loop control unit, an open detector, a short detector and a voltage detector. The open detector and the short detector are utilized for detecting LED open and LED short for the plurality of LED strings, respectively. The voltage detector is coupled to the open detector, the short detector and the voltage converter, and is utilized for generating a reset signal to the short detector according to an output voltage of the voltage converter when the LED open occurs on the plurality of LED strings, so as to initiate the LED short detection for the plurality of LED strings again.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an LED device and related method, and more particularly, to an LED device with a simultaneous open and short detection function and related method.

2. Description of the Prior Art

Light emitting diodes (LEDs) used as light sources has become popular in recent years. For example, cold cathode fluorescent lamps (CCFLs) are conventionally used as a light source in a backlight module of a liquid crystal display. However, LEDs have gradually replaced CCFLs as the light source of the backlight module due to continuously rising luminous efficiency and decreasing cost.

In an LED driving circuit of the prior art, if LED open occurs on an LED string, since a corresponding output channel of the LED driving circuit is floating, the LED driving circuit would have electric leakage, which deteriorates conversion efficiency of the circuit or results in abnormal operation of a voltage conversion loop. Besides, if LED short occurs on an LED string, i.e. cross voltages of some LEDs are zero, headroom voltages of current driving elements would be raised correspondingly, which results in higher power consumption of the current driving elements and deteriorates the conversion efficiency of the circuit as well. Therefore, the LED driving circuit should have LED open and LED short detection mechanism.

Please refer toFIG. 1.FIG. 1is a schematic diagram of an LED driving circuit10according to the prior art. The LED driving circuit10is utilized for driving an LED module11. As shown inFIG. 1, the LED module11includes parallel-connected LED strings C1˜Cm, and each LED string further includes a plurality of series-connected LEDs. The LED driving circuit10includes a voltage converter12, a current driving unit13and a loop control unit14. The voltage converter12is utilized for converting an input voltage V1to an output voltage V2according to a voltage control signal VCTRL so as to drive the LED module11. The current driving unit13is utilized for sinking fixed driving currents Id1˜Idm from the LED module11. The loop control unit14controls voltage conversion of the voltage converter12according to voltage differences between negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm and a default reference voltage VREF, for stabilizing a voltage level of the output voltage V2.

Moreover, the loop control unit14further includes a voltage selector142, an error amplifier144and a conversion controller146. The voltage selector142is coupled to the LED strings C1˜Cm, and is utilized for selecting a lowest voltage of the negative electrode voltages VHR1˜VHRm as a feedback voltage VFB. The error amplifier144is coupled to the voltage selector142and the reference voltage VREF, and is utilized for generating an error voltage signal VERR according to voltage difference between the feedback voltage VFB and the reference voltage VREF. The conversion controller146is coupled to the error amplifier144and the voltage converter12, and is utilized for generating a voltage control signal VCTRL according to the error voltage signal VERR.

Therefore, through the loop control unit14, the LED driving circuit10can lock the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm, i.e. the headroom voltages of the current driving elements, and the output voltage V2of the voltage converter12within a sensible range.

In this case, the LED driving circuit10further includes an open detector15and a short detector16, which are utilized for performing LED open detection and LED short detection on the LED strings C1˜Cm, respectively. Since the headroom voltages of the current driving elements would be pulled to a low voltage level when the LED strings C1˜Cm have LED open, the open detector15can thus determine the LED open occurring on the LED strings C1˜Cm according to whether the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm are lower than a certain low threshold voltage. Of course, the said low threshold voltage cannot be set higher than the headroom voltages of the current driving elements under normal operation for preventing from false LED open detection during the normal operation situations. On the contrary, when the LED strings C1˜Cm have LED short, i.e. cross voltages of some LEDs are zero, the headroom voltages of the current driving elements would rise correspondingly. Thus, the short detector16can determine the LED short occurring on the LED strings C1˜Cm according to whether the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm are higher than a certain high threshold voltage. Similarly, the said high threshold voltage cannot be set lower than the headroom voltages of the current driving elements under the normal operation for preventing from false short detection during the normal operation situations.

However, the LED driving circuit10may erroneously determine the LED short occurring on the LED strings C1˜Cm when simultaneously performing the LED open and short detection on the LED strings C1˜Cm. For example, when the LED string C1has the LED open, the headroom voltage of the current driving element is pulled to a low voltage level (ex. a ground voltage). Thus, the voltage selector142would select the negative electrode voltage VHR1of the LED string C1as the feedback voltage VFB, such that the output voltage V2of the voltage converter12is raised. Under this situation, since the cross voltages of the LEDs are fixed, the negative electrode voltages VHR2˜VHRm of the LED strings C2˜Cm would follow the output voltage V2to rise above the said certain high threshold voltage, which results in false determination of the short detector16.

In other words, when the LED open and the LED short detection are simultaneously performed on the LED strings, the prior art may have false LED short detection immediately after the LED open is detected on some of the LED strings.

SUMMARY OF THE INVENTION

It is therefore an objective of the present invention to provide an LED device with a simultaneous open and short detection function and related method.

The present invention discloses an LED device with a simultaneous open and short detection function. The LED device includes a plurality of LED strings, a voltage converter, a current driving unit, a loop control unit, an open detector, a short detector and a voltage detector. Each LED string of the plurality of LED strings has a positive electrode and a negative electrode. The voltage converter is coupled to the positive electrodes of the plurality of LED strings, and is utilized for converting a first voltage to a second voltage according to a voltage control signal. The current driving unit is coupled to the negative electrodes of the plurality of LED strings, and is utilized for providing a plurality of driving currents to the plurality of LED strings. The loop control unit is coupled to the plurality of LED strings and the voltage converter, and is utilized for generating the voltage control signal according to the negative electrode voltages of the plurality of LED strings. The open detector is coupled to the plurality of LED strings and the loop control unit, and is utilized for performing LED open detection on the plurality of LED strings according to the negative electrode voltages of the plurality of LED strings. The short detector is coupled to the plurality of LED strings and the loop control unit, and is utilized for performing LED short detection on the plurality of LED strings according to the negative electrode voltages of the plurality of LED strings. The voltage detector is coupled to the open detector, the short detector and the voltage converter, and is utilized for generating a reset signal to the short detector for restarting the LED short detection on the plurality of LED strings according to level variation of the second voltage when the open detector detects LED open on the plurality of LED strings.

The present invention also discloses a method of simultaneously detecting open and short for an LED device. The LED device includes a plurality of LED strings and a voltage converter. Each LED string of the plurality of LED strings has a positive electrode and a negative electrode. The voltage converter is coupled to the positive electrodes of the plurality of LED strings, and is utilized for converting a first voltage to a second voltage. The method includes performing LED open and LED short detection on the plurality of LED strings according to negative electrode voltages of the plurality of LED strings; and restarting the LED short detection on the plurality of LED strings according to level variation of the second voltage when the open detector detects LED open on the plurality of LED strings.

The present invention also discloses an LED device with a simultaneous open and short detection function. The LED device includes a plurality of LED strings, a voltage converter, a current driving unit, a loop control unit and an open and short detector. Each LED string of the plurality of LED strings has a positive electrode and a negative electrode. The voltage converter is coupled to the positive electrodes of the plurality of LED strings, and is utilized for converting a first voltage to a second voltage. The current driving unit is coupled to the negative electrodes of the plurality of LED strings, and is utilized for providing a plurality of driving currents to the plurality of LED strings. The loop control unit is coupled to the plurality of LED strings and the voltage converter, and is utilized for generating the voltage control signal according to negative electrode voltages of the plurality of LED strings. The open and short detector is coupled to the plurality of LED strings, the loop control unit and the voltage converter, and is utilized for performing LED open and LED short detection on the plurality of LED strings according to the negative electrode voltages of the plurality of LED strings and a level variation trend of the second voltage.

The present invention also discloses a method of simultaneously detecting open and short for an LED device. The LED device includes a plurality of LED strings and a voltage converter. Each LED string of the plurality of LED strings has a positive electrode and a negative electrode. The voltage converter is coupled to the positive electrode of the plurality of LED strings, and is utilized for converting a first voltage to a second voltage according to a voltage control signal. The method includes generating the voltage control signal according to the negative electrode voltages of the plurality of LED strings; and performing LED open and LED short detection on the plurality of LED strings according to the negative electrode voltages of the plurality of LED strings and a level variation trend of the second voltage.

DETAILED DESCRIPTION

Please refer toFIG. 2.FIG. 2is a schematic diagram of an LED device20with a simultaneous open and short detection function according to a first embodiment of the present invention. The LED device20includes parallel-connected LED strings C1˜Cm, a voltage converter21, a current driving unit22, a loop control unit23, an open detector24, a short detector25and a voltage detector26. The voltage converter21is coupled to positive electrodes of the LED strings C1˜Cm, and is utilized for converting a first voltage V1to a second voltage V2according to a voltage control signal VCTRL and outputting the second voltage V2as a stable driving voltage of the LED strings C1˜Cm. The current driving unit22is coupled to negative electrodes of the LED strings C1˜Cm, and is utilized for providing fixed driving currents Id1˜Idm to the LED strings C1˜Cm. The loop control unit23is coupled to the LED strings C1˜Cm and the voltage converter21, and is utilized for generating the voltage control signal VCTRL according to negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm. The open detector24is coupled to the LED strings C1˜Cm and the loop control unit23, and is utilized for performing LED open detection on the LED strings C1˜Cm according to the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm. The short detector25is coupled to the LED strings C1˜Cm and the loop control unit23, and is utilized for performing short detection on the LED strings C1˜Cm according to the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm. The voltage detector26is coupled to the open detector24, the short detector25and the voltage converter26, and is utilized for generating a reset signal RST to the short detector25for restarting the LED short detection on the LED strings C1˜Cm according to level variation of the second voltage V2when the open detector24detects LED open occurring on the LED strings C1˜Cm.

Therefore, when the LED device20simultaneously performs the LED open and LED short detection on the LED strings C1˜Cm, if the LED open is detected occurring on the LED strings C1˜Cm, the embodiment of the present invention generates and sends the reset signal RST to the short detector25according to the level variation of the second voltage V2, so as to restart the LED short detection on the LED strings C1˜Cm. Accordingly, the embodiment of the present invention can avoid false LED short detection that happens immediately after occurrence of the LED open is detected.

Preferably, the loop control unit23further includes a voltage selector232, an error amplifier234and a conversion controller236. The voltage selector232is coupled to the LED strings C1˜Cm, and is utilized for selecting a lowest voltage of the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm as a feedback voltage VFB. The error amplifier234is coupled to the voltage selector232and a reference voltage VREF, and is utilized for generating an error voltage signal VERR according to voltage difference between the feedback voltage VFB and the reference voltage VREF. The conversion controller236is coupled to the error amplifier234and the voltage converter21, and is utilized for generating the voltage control signal VCTRL according to the error voltage signal VERR, to control conversion operation of the voltage converter21. As for detailed operation of the LED device20, please refer to the following description.

Please refer toFIG. 3, which is a schematic diagram of a process30for the LED device20simultaneously detecting LED open and short according to an embodiment of the present invention. The process30is utilized for realizing an operation process of the LED device20, and includes the following steps:

Step310: Perform the LED open and LED short detection on the LED strings C1˜Cm according to the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm.

Step320: Restart the LED short detection on the LED strings C1˜Cm according to the level variation of the second voltage V2when detecting the LED open occurring on the LED strings C1˜Cm.

According to the process30, the LED open and LED short detection is firstly performed on the LED strings C1˜Cm according to the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm. When the LED strings C1˜Cm are detected to have the LED open, the LED short detection of the LED strings C1˜Cm is restarted according to the level variation of the second voltage V2, for preventing the LED short detection from being erroneously determined after the LED open occurs on the LED strings.

As stated in the prior art, when the LED open occurs on the LED strings C1˜Cm, the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm, i.e. the headroom voltages of the current driving elements, would be pulled to a low voltage level such as a ground voltage level, for example. Thus, the open detector24can determine the LED open occurring on the LED strings C1˜Cm according to whether the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm are lower than a first threshold voltage. On the contrary, when the LED short occurs on the LED stings C1˜Cm, the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm would be raised correspondingly. Thus, the short detector25can determine the LED short occurring on the LED strings C1˜Cm according to whether the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm are higher than a second threshold voltage. Of course, the said first threshold voltage cannot be set higher than the headroom voltages of the current driving elements under normal operation, and the second threshold voltage cannot be set lower than the headroom voltages of the current driving elements under the normal operation, so as to prevent from false detection during the normal operation situations.

Besides, since the voltage selector232selects the negative electrode voltage of which the LED string has the LED open as the feedback voltage VFB, the output voltage V2of the voltage converter21would be raised. Therefore, the voltage detector26can detect whether the voltage level of the output voltage V2is higher than a third threshold value to generate the reset signal RST, so as to restart the LED short detection on the LED strings.

For example, please refer toFIG. 4, which illustrates a situation where the LED short detection is restarted when the LED open occurs on the LED string C1according to an embodiment of the present invention. As shown inFIG. 4, when the LED open occurs on the LED string C1, the negative voltage VHR1would be pulled to a low voltage level, ex. a ground voltage. Thus, the voltage selector232selects the negative electrode voltage VHR1as the feedback voltage VFB, such that the output voltage V2of the voltage converter21is raised. When the output voltage V2is higher than the third threshold value, the voltage detector26immediately generates the reset signal RST to restart the LED short detection on the LED strings C1˜Cm. Meanwhile, the loop control unit23performs over voltage protection on the output voltage V2to maintain the output voltage V2within a sensible voltage range.

Certainly, the process30can further include the following steps: cutting off electrical connection between the loop control unit23and the LED string having the LED open when the LED open is detected on the LED strings C1˜Cm; and cutting off electrical connection between the current driving unit22and the LED string having the LED short when the LED short is detected on the LED strings C1˜Cm. The above operation is well-known to those skilled in the art, and thus is not narrated herein.

In summary, when the LED open and short detection are simultaneously performed on the LED strings, the embodiment of the present invention restarts the LED short detection for the LED strings C1˜Cm according to the voltage variation of the output voltage V2immediately after the LED open is detected on the LED strings, so as to prevent the LED short detection from being erroneously determined. Accordingly, the incapability of simultaneously performing the LED open and LED short detection in the prior art can be improved.

Please refer toFIG. 5.FIG. 5is a schematic diagram of an LED device50with a simultaneous open and short detection function according to a second embodiment of the present invention. The LED device50includes parallel-connected LED strings C1˜Cm, a voltage converter51, a current driving unit52, a loop control unit53and an open and short detector54. The voltage converter51, the current driving unit52and the loop control unit53are similar to the voltage converter21, the current driving unit22and the loop control unit23inFIG. 2, and are not narrated again herein. The open and short detector54is coupled to the LED strings C1˜Cm, the loop control unit53and the voltage converter54, and is utilized for performing LED open and LED short detection on the LED strings C1˜Cm according to level variation trends of both the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm and the second voltage V2.

Since the cross voltages of the LEDs are fixed, the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm and the output voltage V2of the voltage converter51would have the same level variation trends under normal operation, i.e. no LED string has LED open or LED short. In this case, when the level variation trends of the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm and the second voltage V2are different, the embodiment of the present invention can detect the LED open or the LED short on the LED strings C1˜Cm accordingly. As a result, the incapability of simultaneously performing the LED open and short detection on the LED strings can also be improved. As for detailed operation of the LED device50, please refer to the following description.

Please refer toFIG. 6.FIG. 6is a schematic diagram of a process60for the LED device50simultaneously performing LED open and short detection according to an embodiment of the present invention. The process60is utilized for realizing an operation process of the LED device50, and includes the following steps:

Step610: Generate the voltage control signal CVTRL according to the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm.

Step620: Perform the LED open and LED short detection on the LED strings C1˜Cm according to the level variation trends of the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm and the second voltage V2.

According to the process60, the voltage control signal CVTRL is generated according to the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm. Then, the LED open and LED short detection can be performed on the LED strings C1˜Cm according to the level variation trends of the negative electrode voltages VHR1˜VHRm of the LED strings C1˜Cm and the second voltage V2.

In other words, after the voltage conversion loop is established, the LED open and LED short detection can be performed on the LED strings C1˜Cm by detecting whether the voltage variation trends of the negative electrode voltages VHR1˜VHRm and the second voltage V2are the same. For example, please refer toFIG. 7, which illustrates the level variation trends of the negative electrode voltage VHRx of the LED string Cx and the output voltage V2of the voltage converter51when the LED string Cx has LED open or LED short. As mentioned above, when the LED open occurs on the LED string Cx, the negative electrode voltage VHRx of the LED string Cx would be pulled to a low voltage level such as a ground voltage level, for example. Thus, the voltage selector532would select the negative electrode voltage VHRx as the feedback voltage VFB, so as to raise the output voltage V2of the voltage converter51. On the contrary, when the LED short occurs on the LED string Cx, i.e. the cross voltages of some LEDs in the LED string Cx are zero, the negative electrode voltage VHRx would then be raised correspondingly.

Therefore, when detecting the negative electrode voltage VHRx of the LED string Cx descending and the level of the second voltage V2rising, the LED open and LED short detector54determines that the LED open occurs on the LED string Cx. On the contrary, when detecting the negative electrode voltage VHRx of the LED string Cx rising and the level of the second voltage V2unchanged, the LED open and LED short detector determines that the LED short occurs on the LED string Cx. By such detection mechanism, the incapability of simultaneously performing the LED open and LED short detection on the LED strings in the prior can be improved.

Of course, the process60according to the embodiment of the present invention also includes the following steps: cutting off electrical connection between the loop control unit53and the LED string having the LED open when the LED open is detected on the LED strings C1˜Cm; and cutting off electrical connection between the current driving unit52and the LED string having the LED short when the LED short is detected on the LED strings C1˜Cm. The above operation is known by those skilled in the art, and is not narrated herein again.

To sum up, the present invention provides the method of simultaneously performing LED open and short detection for the LED device to prevent the LED short from being erroneously determined after occurrence of the LED open, which is a major problem in the prior art.