TWI432094B - Lamp brightness controlling device - Google Patents

Description

Light source brightness control device

The invention relates to a light source brightness control device.

At present, a plurality of bulbs are generally disposed as a light source in a backlight module of a liquid crystal display, and the bulb is generally a Cold Cathode Fluorescent Lamp (CCFL). The light source brightness control device is for controlling the brightness of the CCFL within a certain range. In the safety specification test, according to the principle of single error, it is only necessary to randomly select a CCFL, and short-circuit the high-voltage end and the low-voltage end of the CCFL through a wire to detect the current flowing through the CCFL to see if the current is safe. Within the scope of the specification. The previous light source brightness control device electrically connects the plurality of CCFLs to a control chip through a tube flow feedback circuit for feeding back the lowest current flowing through the plurality of CCFLs, The current when the high and low voltage terminals of the CCFL are shorted is much smaller than the rated current of the CCFL. Therefore, as long as there is a short circuit between the high and low voltage terminals of the CCFL, the current detected by the tube current feedback circuit is The current flowing through the CCFL when shorted between the high and low voltage terminals of the CCFL. Storing a reference current in the control chip, the reference current is equal to the rated current of the CCFL, and if the current value detected by the tube flow feedback circuit is less than the rated current of the CCFL, the control chip will The current in each CCFL is increased, so that the current of the CCFL in normal operation will exceed the rated current and be easily damaged.

In view of this, it is necessary to provide a light source brightness control device that protects other light sources from normal damage when the high voltage end and the low voltage end of one of the light sources are shorted.

A light source brightness control device for controlling the brightness of at least two light sources within a normal range. The at least two light sources are cold cathode fluorescent tubes, and each of the light sources includes a high voltage end and a low voltage end. The light source brightness control device is further configured to protect other light sources from normal damage when the high voltage end and the low voltage end of one of the light sources are shorted. The light source brightness control device includes at least two grounding resistors, at least two first diodes, a first control circuit, a second control circuit, and at least two third diodes. The at least two light sources are respectively in one-to-one correspondence with the at least two grounding resistors and the at least two first diodes. The anode of each of the first diodes is electrically connected to the low voltage end of the corresponding light source and the corresponding grounding resistance. The first control circuit includes a first voltage dividing resistor, a second voltage dividing resistor and a first control chip, and one end of the first voltage dividing resistor and the cathode of the at least two first diodes The other end is electrically connected to the first control chip and the second voltage dividing resistor, and the other end of the second voltage dividing resistor is grounded. The first voltage dividing resistor intersects the second voltage dividing resistor to form a fourth node. The first control chip is configured to detect a voltage of the fourth node, and the first control chip internally stores a first reference voltage, where the first reference voltage is when at least one light source is working normally. The voltage of the fourth node is described. If the voltage of the fourth node is greater than or equal to the first reference voltage, it indicates that at least one other light source is working normally, and the first control chip does not issue a control signal to prevent the normally working light source from being damaged due to excessive current. The cathodes of the at least two third diodes are respectively electrically connected to the corresponding low voltage ends, and the anodes of the at least two third diodes intersect to form a fifth node, the fifth node and the first The second control circuit is electrically connected; the second control circuit is configured to detect a voltage of the fifth node, and the second control circuit stores a second The reference voltage, when the voltage of the fifth node is less than the second reference voltage, the second control chip sends a control signal to stop the at least two driving circuits.

The light source brightness control device of the present invention uses at least two diodes to feed back the maximum current flowing through the at least two light sources to the first control circuit, so that in the safety specification test, the control chip does not Because the high voltage end of one of the light sources is shorted to the low voltage end, the currents in the at least two light sources are simultaneously increased, thereby effectively protecting other light sources from normal operation without being damaged.

100‧‧‧Light source brightness control device

210‧‧‧First light source

220‧‧‧second light source

11‧‧‧First drive circuit

12‧‧‧Second drive circuit

31‧‧‧First grounding resistance

32‧‧‧Second grounding resistance

41‧‧‧First Diode

42‧‧‧second diode

51‧‧‧ Third Dipole

52‧‧‧Fourth dipole

60‧‧‧First control circuit

61‧‧‧First voltage divider resistor

62‧‧‧Second voltage divider resistor

63‧‧‧First control chip

70‧‧‧Second control circuit

71‧‧‧DC bias source

73‧‧‧ Third voltage divider resistor

75‧‧‧second control chip

N1‧‧‧ first node

N2‧‧‧ second node

N3‧‧‧ third node

N4‧‧‧ fourth node

N5‧‧‧ fifth node

1 is a circuit diagram of a light source brightness control device according to a preferred embodiment of the present invention.

The invention will be further described in detail below with reference to the accompanying drawings.

1 is a light source brightness control apparatus 100 for controlling the brightness of a plurality of light sources in a backlight module (not shown), and protecting one of the light sources when the light source is abnormal. Other light sources work normally and are not damaged. In the present embodiment, a backlight module including two light sources (ie, the first light source 210 and the second light source 220) will be described as an example.

The light source brightness control device 100 includes a first driving circuit 11, a second driving circuit 12, a first grounding resistor 31, a second grounding resistor 32, a first diode 41, and a second diode. 42. A third diode 51, a fourth diode 52, a first control circuit 60, and a second control circuit 70.

The first light source 210 and the second light source 220 have the same model, and both are lamps that require high-voltage high-frequency electric field excitation, but the brightness of the tube depends on the electricity flowing through it. Flow to control. The lamp tube comprises a high voltage end and a low voltage end, and has a characteristic that when a short wire is connected between the high voltage end and the low voltage end of the lamp tube, most of the current passes through the wire, but A part of the current will flow through the lamp, and the current of the lamp will be much smaller than the current in the normal working state (ie, the lamp operates at the rated current), so the brightness of the lamp itself will become lower. . In the embodiment, the first light source 210 and the second light source 220 are both Cold Cathode Fluorescent Lamps (CCFLs). When the first light source 210 and the second light source 220 are normally operated, the rated current is I1, and the currents when the high voltage end and the low voltage end of the first light source 210 and the second light source 220 are short-circuited are both I2. I1 is much larger than I2. In the present embodiment, the I1 is 5 to 9 mA, and the I2 is 0.01 to 0.03 mA.

The first light source 210 includes a first high voltage end 211 and a first low voltage end 212, and the second light source 220 includes a second high voltage end 221 and a second low voltage end 222.

The first driving circuit 11 and the second driving circuit 12 are electrically connected to the first high voltage end 211 and the second high voltage end 221, respectively, for driving the first light source 210 and the second light source. 220 light. In the embodiment, the first driving circuit 11 and the second driving circuit 12 are both an inverter for converting direct current into alternating current of 40 kV to 50 kV.

One end of the first grounding resistor 31 is electrically connected to the first low voltage end 212, respectively, to form a first node N1. The second grounding resistor 32 is electrically connected to the second low voltage terminal 222 to form a second node N2. The other ends of the first grounding resistor 31 and the second grounding resistor 32 are respectively grounded; the voltages of the first node N1 and the second node N2 are respectively the two ends of the first grounding resistor 31 and the second grounding resistor 32. Voltage. The resistance of the first grounding resistor 31 is represented by R1, and the resistance of the second grounding resistor 32 is represented by R2. Shown, and R1 = R2. In the present embodiment, both R1 and R2 are 1 kΩ.

The first low voltage terminal 212 is electrically connected to the first control circuit 60 through a first diode 41. The second low voltage terminal 222 is electrically connected to the first control circuit 60 via a second diode 42. The anodes of the first diode 41 and the second diode 42 are electrically connected to the first low voltage end 212 and the second low voltage end 222, respectively, the first diode 41 and the second diode. The cathodes of 42 intersect to form a third node N3, which is then electrically coupled to the first control circuit 60.

The first control circuit 60 is configured to detect a maximum current flowing through the first light source 210 and the second light source 220, convert the maximum current signal into a voltage signal, and then determine whether the target is based on the detection result. The first light source 210 and the second light source 220 perform current compensation to maintain the brightness of the first light source 210 and the second light source 220 within a certain range. The first control circuit 60 includes a first voltage dividing resistor 61, a second voltage dividing resistor 62 and a first control wafer 63. One end of the first voltage dividing resistor 61 is electrically connected to the cathode of the first diode 41, and the other end is electrically connected to one end of the first control wafer 63 and the second voltage dividing resistor 62 at the same time. The other end of the second voltage dividing resistor 62 is grounded. The first voltage dividing resistor 61 and the second voltage dividing resistor 62 intersect to form a fourth node N4. The resistance of the first voltage dividing resistor 61 is represented by R3, and the resistance of the second voltage dividing resistor 62 is represented by R4. A first reference voltage U10 is stored in the first control chip 63 for detecting the voltage of the fourth node N4, and the voltage of the fourth node N4 is compared with the first reference voltage U10. Compare and send a control signal based on the comparison. The first reference voltage U10 is the first light source 210 and the second light source 220. When one of the light sources operates normally, and the high and low voltage ends of the other light source are shorted, the first control chip 63 The detected voltage value of the fourth node N4.

The specific analysis is as follows: (1) when the first light source 210 works normally, and the high and low voltage ends of the second light source 220 are short-circuited, the current I1 flowing through the first light source 210 flows through the second When the current in the light source 220 is large, the voltage of the first node N1 is greater than the voltage of the second node N2. Since the third node N3 is grounded through the first voltage dividing resistor 61 and the second voltage dividing resistor 62, when no current flows through the first voltage dividing resistor 61 and the second voltage dividing resistor 62, The voltage of the third node N3 is zero. At this time, since the voltage difference between the first diode 41 and the second diode 42 is larger, the first diode 41 is turned on first, so that the voltage of the third node N3 is slightly smaller than the first The voltage of the node N1 (since the first diode 41 is turned on, there is a small voltage drop, such as 0.3V), the voltage of the third node N3 is greater than the voltage of the second node N2. The second diode 42 is turned off. At this time, the current flowing into the second voltage dividing resistor 62 is the current I1 flowing through the first light source 210, so the voltage across the second voltage dividing resistor 62 (that is, the voltage of the fourth node N4 is U11) is U11. =R4*I1.

(2) If both the first light source 210 and the second light source 220 are working normally, the current flowing through the first light source 210 and flowing through the second light source 220 is I1, and the first node N1 The voltage is equal to the voltage of the second node N2, and the voltage difference between the first diode 41 and the second diode 42 is equal, so that the first diode 41 and the second diode 42 is simultaneously turned on, and the current flowing into the second voltage dividing resistor 62 is the sum of the current flowing through the first light source 210 and the current flowing through the second light source 220, and the second voltage dividing resistor The voltage across 62 (ie, the voltage at the fourth node N4 is) U12 = R4 * (I1 + I1). Obviously, U12>U11.

(3) if both the high and low voltage ends of the first light source 210 and the second light source 220 are shorted, the current flowing through the first light source 210 and flowing through the second light source 220 is I2, the voltage of the first node N1 is equal to the voltage of the second node N2, and the voltage difference between the first diode 41 and the second diode 42 is equal, so that the first diode The body 41 and the second diode 42 are simultaneously turned on. At this time, the current flowing into the second voltage dividing resistor 62 is a current flowing through the first light source 210 and a current flowing through the second light source 220. And, at this time, the current I2 flowing through the first light source 210 and the second light source 220 is very small, much smaller than I1, and the voltage across the second voltage dividing resistor 62 (that is, the voltage of the fourth node N4) Is) U13=R4*(I2+I2). Obviously, U13<U11.

In summary, if the voltage of the fourth node N4 is greater than or equal to the first reference voltage U10, it indicates that at least one other light source is working normally, and the first control chip 63 does not operate to prevent the normal working light source from being current. If the voltage of the fourth node N4 is less than the first reference voltage U10, it indicates that both the high and low voltage ends of the first light source 210 and the second light source 220 are shorted, the first control chip The control signal is sent to increase the current of the first light source 210 and the second light source 220 to increase the brightness of the first light source 210 and the second light source 220.

The first low voltage terminal 212 is electrically connected to the second control circuit 70 through the third diode 51, and the second low voltage terminal 222 passes through the fourth diode 52 and the second control circuit. 70 electrical connections. The cathodes of the third diode 51 and the fourth diode 52 are electrically connected to the first low voltage end 212 and the second low voltage end 222, respectively, and the third diode 51 and the The fifth node N5 is formed at the intersection of the anodes of the fourth diode 52, and the fifth node N5 is electrically connected to the second control circuit 70.

The second control circuit 70 is configured to detect whether the high voltage end of the first light source 210 or the second light source 220 is disconnected from the corresponding driving circuit, and if one of the high voltage ends of the light source is disconnected from the corresponding driving circuit, The second control circuit 70 sends a control signal. Stopping the first driving circuit 11 and the second driving circuit 12 to prevent the first driving circuit 11 and the second driving circuit 12 from being in the first light source 210 or the second light source 220 When the high voltage end is disconnected, the high voltage discharge is continuously performed, causing damage to the human body.

The second control circuit 70 includes a DC bias source 71, a third voltage dividing resistor 73, and a second control wafer 75. The DC bias source 71 is electrically connected to the fifth node N5 through the third voltage dividing resistor 73. The resistance of the third voltage dividing resistor 73 is represented by R5. The second control wafer 75 is electrically connected to the fifth node N5. The DC bias source 71 is configured to provide a DC voltage VCC and the voltage supplied is lower than the voltage of the node between the normally operating source and its corresponding ground resistance (eg, if the first source 210 is operating normally) The voltage of the VCC is lower than the voltage of the first node N1, so that when the first light source 210 is working normally, the third diode 51 is turned off; when the second light source 220 is working normally At the time, the fourth diode 52 is turned off. Therefore, when both the first light source 210 and the second light source 220 are normally operated, the voltage of the fifth node N5 is equal to the voltage VCC provided by the DC bias source 71. A second reference voltage U22 is stored in the second control wafer 75, wherein the second reference voltage U22 is equal to the voltage VCC of the DC bias source 71. The second control chip 75 is further configured to detect a voltage of the fifth node N5. If the voltage of the fifth node N5 is less than the second reference voltage U22, the second control chip 75 sends a control signal. The first driving circuit 11 and the second driving circuit 12 are stopped.

The specific analysis is as follows: when the first light source 210 and the second light source 220 are both normally working, the third diode 51 and the fourth diode 52 are both turned off, then the third partial pressure There is no current in the resistor 73, causing the voltage of the fifth node N5 to be equal to the voltage VCC (ie, the second reference voltage U22) provided by the DC bias source 71. When the first light source 210 is normally operated, and the second high voltage terminal 221 of the second light source 220 is disconnected from the second driving circuit 12, the voltage of the first node N1 is greater than the voltage of the DC bias source 71. The voltage of the second node N2 is zero, the third diode 51 is turned off, and the fourth diode 52 is turned on. At this time, the DC bias source 71 and the third voltage dividing resistor are turned on. 73. The second grounding resistor 32 forms a loop, and the voltage of the fifth node N5 is the voltage of the second grounding resistor 32. Obviously smaller than the second reference voltage U22; similarly, if the high voltage ends of the first light source 210 and the second light source 220 are disconnected from the corresponding driving circuit, the first node N1 and the first The voltages of the two nodes N2 are all zero, and the third diode 51 and the fourth diode 52 are both turned on. At this time, the voltage of the fourth node N4 is the first ground resistance 31 and the second. The voltage obtained after the grounding resistors 32 are connected in parallel ,(among them And U52 is also smaller than the second reference voltage U22. Therefore, if the voltage of the fifth node N5 is smaller than the second reference voltage U22, it indicates that the high voltage end of the at least one light source is disconnected from the corresponding driving circuit. When the second control chip 75 sends a control signal, the first driving circuit 11 and the second driving circuit 12 are stopped. In the present embodiment, the voltage supplied by the DC bias source 71 is 24V. The resistance of the third voltage dividing resistor 73 is 10 kΩ.

The working process of the light source brightness control device 100 is as follows:

(1) If the first light source 210 is normally operated in the safety specification test, and the high and low voltage ends of the second light source 220 are short-circuited, the first diode 41 is turned on. The second diode 42 is turned off, so that the current of the first light source 210 enters the first control circuit 60, and the current of the second light source 220 does not enter the first control circuit 60, so that the first The voltage detected by a control chip 63 is less than the first reference voltage U10, and the first control chip 63 does not emit a control signal, and does not increase the current of the first light source 210 and the second light source 220, and protects The first light source 210.

(2) if the high and low voltage ends of the first light source 210 and the second light source 220 are simultaneously shorted during use of the backlight module (not shown), flowing through the first light source 210 and the The current in the second light source 220 is greatly reduced, and the brightness of the first light source 210 and the second light source 220 is darkened. At this time, the first diode 41 and the second diode 42 are both The first control circuit 60 can send a control signal to the first light source 210 and the second light source 220 according to the detection result of the fourth node N4 being smaller than the detection result of the first reference voltage U10. The current in the current is increased, and the brightness in the first light source 210 and the second light source 220 is restored to a normal range.

(3) If the first light source 210 is normally operated, and the second high voltage terminal 221 of the second light source 220 is disconnected from the second driving circuit 12, the fourth diode 52 is turned on. The voltage of the five-node N5 is smaller than the second reference voltage U22, so the second control chip 75 sends a control signal to stop the first driving circuit 11 and the second driving circuit 12. Similarly, if the high voltage ends of the first light source 210 and the second light source 220 are both disconnected from the corresponding driving circuit, the third diode 51 and the fourth diode 52 are both turned on, then the first The voltage of the five-node N5 is still smaller than the second reference voltage U22, so the second control chip 75 also sends a control signal to stop the first driving circuit 11 and the second driving circuit 12. In summary, it can be known that as long as the high voltage end of one light source is disconnected from the corresponding driving circuit, the second The control chip 75 sends a control signal to stop the operation of the first driving circuit 11 and the second driving circuit 12 to prevent leakage, thereby better protecting the safety of the user.

It can be understood that, in other embodiments, if the number of the light sources in the backlight module (not shown) is more than two, the circuit connection relationship of the other light sources and the first light source 210 and the second The light source 220 is the same, that is, the low voltage end of each light source is electrically connected to the first control circuit through a fifth diode, and is also electrically connected to the second control circuit through a sixth diode. That is, the anode of the fifth diode and the cathode of the sixth diode are electrically connected to the low voltage end, and the cathode of the fifth diode is electrically connected to the first control circuit, the The anode of the hexa diode is electrically connected to the second control circuit. And the low voltage side of each of the light sources is also electrically connected to a grounding resistor.

The light source brightness control device of the present invention uses at least two diodes to feed back the maximum current flowing through the first light source and the second light source to the first control wafer, so that in the safety specification test, the first control The wafer does not increase the current in the normally working light source because the high and low voltage ends of one of the light sources are short-circuited, thereby effectively protecting the light source in a normal working state from being damaged; and the light source protection circuit The second control chip can also be detected when the high voltage end of the first light source and the second light source is disconnected from the corresponding driving circuit, so that the high voltage end of at least one light source is disconnected from the corresponding driving circuit. The instruction causes the first driving circuit and the second driving circuit to stop working to prevent damage caused by the user.

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by persons skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

100‧‧‧Light source brightness control device

210‧‧‧First light source

220‧‧‧second light source

11‧‧‧First drive circuit

12‧‧‧Second drive circuit

31‧‧‧First grounding resistance

32‧‧‧Second grounding resistance

41‧‧‧First Diode

42‧‧‧second diode

51‧‧‧ Third Dipole

52‧‧‧Fourth dipole

60‧‧‧First control circuit

61‧‧‧First voltage divider resistor

62‧‧‧Second voltage divider resistor

63‧‧‧First control chip

70‧‧‧Second control circuit

71‧‧‧DC bias source

73‧‧‧ Third voltage divider resistor

75‧‧‧second control chip

N1‧‧‧ first node

N2‧‧‧ second node

N3‧‧‧ third node

N4‧‧‧ fourth node

N5‧‧‧ fifth node

Claims (6)

A light source brightness control device for controlling brightness of at least two light sources in a normal range, the at least two light sources are cold cathode fluorescent tubes, and each light source comprises a high voltage end and a low voltage end, The light source brightness control device is further configured to protect a normally working light source when the high voltage end and the low voltage end of one of the light sources are shorted; the light source brightness control device includes at least two grounding resistors, at least two first diodes a first control circuit, a second control circuit, and at least two third diodes; the at least two light sources are respectively connected to the at least two grounding resistors and the at least two first diodes Corresponding; the anode of each first diode is electrically connected to the corresponding low voltage end and the corresponding grounding resistance; the first control circuit includes a first voltage dividing resistor, a second voltage dividing resistor and a first control a chip, one end of the first voltage dividing resistor is electrically connected to the cathodes of the at least two first diodes, and the other end is simultaneously electrically connected to the first control chip and the second voltage dividing resistor The other end of the second voltage dividing resistor is grounded; the first voltage dividing resistor intersects the second voltage dividing resistor to form a fourth node; the first control chip is configured to detect the fourth node a voltage, and the first control chip internally stores a first reference voltage, the first reference voltage is a voltage of the fourth node when at least one power source is working normally; and if the voltage of the fourth node is When the first reference voltage is greater than or equal to the first reference voltage, it indicates that at least one other light source is working normally, and the first control chip does not emit a control signal for increasing the current of the at least two light sources, thereby preventing the normal working light source from being excessively current. And being damaged; the cathodes of the at least two third diodes are respectively electrically connected to the corresponding low voltage ends, and the anodes of the at least two third diodes intersect to form a fifth node, the fifth node and The second control circuit is electrically connected; the second control circuit is configured to detect a voltage of the fifth node, and the second control circuit stores a second reference voltage, when the fifth node is Electricity Is less than the second reference voltage, said first The control chip sends a control signal to stop the at least two drive circuits. The light source brightness control device of claim 1, wherein if the voltage of the fourth node is less than the first reference voltage, it indicates that the high and low voltage ends of the at least two light sources are between Shorted, the first control circuit increases the current in the at least two light sources until the voltage of the fourth node increases to the product of the first reference voltage and the number of the light sources . The light source brightness control device of claim 1, wherein the light source brightness control device further comprises at least two first driving circuits, each light source comprising a high voltage end, each driving circuit and a corresponding light source The high voltage end is electrically connected to drive a corresponding one of the light sources to emit light. The light source brightness control device of claim 1, wherein the second control circuit comprises a DC bias source, a third voltage dividing resistor and a second control chip, and the DC bias source passes The third voltage dividing resistor is simultaneously electrically connected to the cathode of the third diode, the cathode of the fourth diode, and the second control wafer. The light source brightness control device of claim 4, wherein the second reference voltage is a voltage of the DC bias source. The light source brightness control device of claim 4, wherein the DC bias source provides a voltage lower than a voltage across the grounding resistor to which the normally operating light source is connected.