CN101399007B - Backlight open-circuit protective circuit - Google Patents
Backlight open-circuit protective circuit Download PDFInfo
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- CN101399007B CN101399007B CN2007100774002A CN200710077400A CN101399007B CN 101399007 B CN101399007 B CN 101399007B CN 2007100774002 A CN2007100774002 A CN 2007100774002A CN 200710077400 A CN200710077400 A CN 200710077400A CN 101399007 B CN101399007 B CN 101399007B
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- circuit
- backlight open
- pulse
- transistor
- width modulator
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Abstract
The invention relates to a backlight open-circuit protective circuit, comprising a plurality of backlight open-circuit detection circuits, an input circuit, a control switch and a pulse-width modulator; wherein, each backlight open-circuit detection circuit comprises a detection output end; the input circuit comprises a plurality of LEDs, a plurality of input resistances and a plurality of integrating capacitors; the control switch comprises a transistor; the pulse-width modulator comprises a control end; the anodes of the LEDs are connected with the input circuit; the cathodes of the LEDs are respectively earthed by the integrating capacitors and the input resistances, and respectively and electrically connected with the detection output ends; a grid electrode of the transistor is connected with a power supply, a source electrode is connected to the anodes of the LEDs of the input circuit, and a drain electrode is connected with the control end. The backlight open-circuit protective circuit has simple structure.
Description
Technical field
The present invention relates to a kind of backlight open circuit protection circuit, particularly a kind of backlight liquid crystal display open loop protection circuit that is used for.
Background technology
Therefore advantages such as LCD has gently, approaches, power consumption is little are widely used in modernized information equipments such as notebook computer, mobile phone, personal digital assistant.Because the liquid crystal molecule itself in the LCD is not luminous, therefore LCD needs to show that by the luminous image of realizing of a backlight module backlight module comprises the pulse-width modulator of a plurality of backlight lamp tubes and these a plurality of backlight lamp tube working currents of adjusting usually.Unexpected when backlight lamp tube job appearance, when causing the output load open circuit of this pulse-width modulator, this pulse-width modulator needs a backlight open circuit protection circuit that it is quit work.
Seeing also Fig. 1, is a kind of electrical block diagram of prior art backlight open circuit protection circuit 100.This backlight open circuit protection circuit 100 comprises four testing circuits 110, an input circuit 130, a pulse-width modulator 150 and a gauge tap 170.
Each testing circuit 110 comprises that a backlight lamp tube 111 and detects output terminal 112.
This input circuit 130 comprises four diodes 131, four biasing resistors 132, four filter capacitors 135, a first transistor 1331, a transistor seconds 1332, one the 3rd transistor 1333 and one the 4th transistors 1334.The source ground of this first transistor 1331, the drain electrode of this first transistor 1331 is electrically connected to the source electrode of this transistor seconds 1332, the drain electrode of this transistor seconds 1332 is electrically connected to the source electrode of the 3rd transistor 1333, the drain electrode of the 3rd transistor 1333 is electrically connected to the source electrode of the 4th transistor 1334, and the drain electrode of the 4th transistor 1334 is output terminals of this input circuit 130.The grid of the first transistor 1331 is via a biasing resistor 132 and a filter capacitor 135 ground connection in parallel, and the negative electricity of a diode 131 is connected to the grid of this first transistor 1331, and the positive pole of this diode 131 is as an input end of this input circuit 130.The grid of this transistor seconds 1332, the 3rd transistor 1333 and the 4th transistor 1334 is also respectively via a biasing resistor 132 and a filter capacitor 135 ground connection in parallel, and be connected respectively to the negative pole of a diode 131, the positive pole of corresponding diode 131 is as an input end of this input circuit 130.So the positive pole of these four diodes 131 is respectively as four input ends of this input circuit 130, and is connected respectively to these four and detects output terminals 112.
This pulse-width modulator 150 comprises a control end 151, when this control end 151 by drop-down when being low-voltage, this pulse-width modulator 150 quits work.
This gauge tap 170 comprises one the 5th transistor 171 and a current-limiting resistance 172, the source ground of the 5th transistor 171, the drain electrode of the 5th transistor 171 is electrically connected to the grid of control end 151, the five transistors 171 of this pulse-width modulator 150 and the drain electrode of the 4th transistor 1334 all is electrically connected to a 5V power supply (pin of this pulse-width modulator 150) via this current-limiting resistance 172.
During these backlight open circuit protection circuit 100 operate as normal, the high voltage of an outside (figure does not show) is loaded into the control end 151 of this pulse-width modulator 150.Simultaneously, four of these four testing circuits 110 detection output terminals 112 are all exported four high voltage signals.These four high voltage signals make this first transistor 1331, transistor seconds 1332, the 3rd transistor 1333 and the 4th all conductings of transistor 1334 by these four diodes 131, then the drain electrode of the 4th transistor 1334 by drop-down be low-voltage, so the 5th transistor 171 is closed.Thereby the control end of this pulse-width modulator 150 151 keeps high voltage, at this moment these pulse-width modulator 150 operate as normal.
When any testing circuit 110 detects backlight lamp tube 111 for open circuit or shorted to earth, detection output terminal 112 ground connection of this testing circuit 110 make one of this first transistor 1331, transistor seconds 1332, the 3rd transistor 1333 and the 4th transistor 1334 close.Because the grid of the 5th transistor 171 and the drain electrode of the 4th transistor 1334 all are electrically connected to a power supply via this current-limiting resistance 172; therefore the grid of the 5th transistor 171 is a high voltage; 171 conductings of the 5th transistor; so this control end 151 that is connected with 171 drain electrodes of the 5th transistor is drawn to be low-voltage; this pulse-width modulator 150 quits work, and realizes the backlight open-circuit defencive function.
In this backlight open circuit protection circuit 100; this input circuit 130 comprises 1331,1332,1333,1,334 four transistors of first, second, third, fourth transistor; the structure more complicated; if and the backlight lamp tube 111 that adopts is when increasing; this input circuit 130 also needs corresponding increase number of transistors, further increases cost.
Summary of the invention
For solving the baroque problem of backlight open circuit protection circuit in the prior art, be necessary to provide a kind of structure better simply backlight open circuit protection circuit.
A kind of backlight open circuit protection circuit comprises a plurality of backlight open-circuit testing circuits, an input circuit, a pulse-width modulator and a gauge tap.Each backlight open-circuit testing circuit comprises that a backlight lamp tube and detects output terminal.This input circuit comprises a plurality of diodes, a plurality of input resistance and a plurality of integrating capacitor.One pulse-width modulator, whether it comprises a control end, be used to control this pulse-width modulator and work.Via this integrating capacitor that is connected in parallel and this input resistance ground connection, the negative pole of these a plurality of diodes also is electrically connected to this a plurality of detection output terminals respectively to the negative pole of these a plurality of diodes respectively.This gauge tap is connected between the positive pole and this control end of these a plurality of diodes, is used for the voltage according to this control end of Control of Voltage of these a plurality of diode cathodes.
A kind of backlight open circuit protection circuit comprises a plurality of backlight open-circuit testing circuits, an input circuit, a pulse-width modulator and a gauge tap.Each backlight open-circuit testing circuit comprises that a backlight lamp tube and detects output terminal.This input circuit comprises a plurality of diodes, a plurality of input resistance and a plurality of integrating capacitor.One pulse-width modulator, whether it comprises a control end, be used to control this pulse-width modulator and work.The negative pole of these a plurality of diodes is respectively via this integrating capacitor ground connection, and is connected to this a plurality of detection output terminals via this input resistance respectively.This gauge tap is connected between the positive pole and this control end of these a plurality of diodes, is used for the voltage according to this control end of Control of Voltage of these a plurality of diode cathodes.
Compare with prior art, the input circuit of above-mentioned backlight open circuit protection circuit can be saved transistor unit, and is therefore simple in structure.
Description of drawings
Fig. 1 is a kind of electrical block diagram of prior art backlight open circuit protection circuit.
Fig. 2 is the electrical block diagram of backlight open circuit protection circuit first embodiment of the present invention.
Fig. 3 is the electrical block diagram of backlight open circuit protection circuit second embodiment of the present invention.
Embodiment
Seeing also Fig. 2, is the electrical block diagram of backlight open circuit protection circuit first embodiment of the present invention.This backlight open circuit protection circuit 200 comprises a plurality of backlight open detection circuit 210, an input circuit 230, a pulse-width modulator 250, a gauge tap 270 and a capacitance 239.
Each backlight open detection circuit 210 comprises that a backlight lamp tube 211 and detects output terminal 212.
This pulse-width modulator 250 comprises a control end 251, when this control end 251 is high voltage, and these pulse-width modulator 250 operate as normal.When this control end 251 was low-voltage, this pulse-width modulator 250 can quit work.
This gauge tap 270 comprises a transistor 271 and a current-limiting resistance 272.The source electrode of this transistor 271 is connected to a 5V direct supply via this current-limiting resistance 272, and source electrode is connected to this input circuit 230, and drain electrode is connected to this control end 251 and via these capacitance 239 ground connection.This 5V direct supply is that the pin by this pulse-width modulator 250 provides.
This input circuit 230 comprises a plurality of diodes 231, a plurality of input resistance 232 and a plurality of integrating capacitor 233.The positive pole of these a plurality of diodes 231 is as the output terminal of this input circuit 230, and all is connected to the source electrode of this transistor 271.The negative pole of these a plurality of diodes 231 is as a plurality of input ends of this input circuit 230, respectively via these integrating capacitor 233 and these input resistance 232 ground connection.The negative pole of these a plurality of diodes 231 is electrically connected to one respectively and detects output terminal 212.
The model of this diode 231 is IN4148, and the resistance value of this input resistance 232 is 1000K Ω, and the resistance value of this current-limiting resistance 272 is 100K Ω, and the capacitance of this integrating capacitor 233 is 0.1 μ F.This transistor 271 is a N channel enhancement mos field effect transistor (N-channel enhancement modemetal-oxide-semiconductor field-effect transistor, N-MOSFET), perhaps be other alternative npn type bipolar transistor.This pulse-width modulator 250 is that the employing model is the integrated circuit of OZ9910G.This backlight 211 be the cold cathode fluorescent lamp pipe (coldcathode fluorescent light, CCFL).Wherein, the forward voltage of this transistor 271 is about 3V, and this transistor was just understood conducting when also promptly voltage difference was not less than 3V between the lock/source of this transistor 271.
During these backlight open circuit protection circuit 200 operate as normal, the high voltage of an outside (figure does not show) is loaded into the control end 251 of this pulse-width modulator 250.Simultaneously, the bigger fluorescent tube sample rate current of a plurality of detection output terminals 212 output one amplitudes of these a plurality of backlight open detection circuit 210.This fluorescent tube sample rate current becomes the dc high voltage of an about 3V after via this input resistance 232 and these integrating capacitor 233 integrations.This 3V dc high voltage is the source electrode that is loaded into this transistor 271 behind the 3.7V by these diode 231 liftings.Because the grid of this transistor 271 is connected to the 5V direct supply, voltage is about 1.3V between this transistorized lock/source, and is not enough so that the source electrode of this transistor 271 and drain electrode conducting.Therefore this transistor 271 is closed, and this control end 251 keeps high voltage, these pulse-width modulation circuit 250 operate as normal.
When any backlight open detection circuit 210 detected backlight lamp tube 211 for open circuit or shorted to earth, the fluorescent tube sample rate current size of detection output terminal 212 outputs of this backlight open detection circuit 210 became 0.Because the positive pole of these a plurality of diodes links together, and makes the cathode voltage of these a plurality of diodes 231 become 0.7V.So the source voltage of this transistor 271 becomes 0.7V.Voltage is about 4.3V between the lock/source of this transistor 271, makes these transistor 271 conductings.Dragged down so be connected to the voltage of this control end 251 in the drain electrode of this transistor 271, this pulse-width modulator 250 quits work, and realizes the backlight open-circuit defencive function.
Seeing also Fig. 3, is the electrical block diagram of backlight open circuit protection circuit second embodiment of the present invention.This backlight open circuit protection circuit 300 comprises a plurality of backlight open detection circuit 310, an input circuit 330, a pulse-width modulator 350 and a gauge tap 370.Each backlight open detection circuit 310 comprises that a backlight lamp tube 311 and detects output terminal 312.
This pulse-width modulator 350 comprises a control end 351, when this control end 351 is high voltage, and these pulse-width modulator 350 operate as normal.When this control end 351 was low-voltage, this pulse-width modulator 350 can quit work.
This gauge tap 370 comprises a transistor 371 and a current-limiting resistance 372.The grid of this transistor 371 is connected to one 5 volts of direct supplys via this current-limiting resistance 372, and source electrode is connected to this input circuit 330, and drain electrode is connected to this control end 351 and via a capacitance 339 ground connection.This 5V direct supply is that the pin by this pulse-width modulator 350 provides.
This input circuit 330 comprises a plurality of diodes 331, a plurality of input resistance 332 and a plurality of integrating capacitor 333.The positive pole of these a plurality of diodes 331 all is connected to the source electrode of this transistor 371.The negative pole of these a plurality of diodes 331 is respectively via these integrating capacitor 333 ground connection, and is electrically connected to one via this input resistance 332 and detects output terminal 312.
Compared to prior art, input circuit 230,330 has been saved transistor unit in the above-mentioned backlight open circuit protection circuit 200,300, so this backlight open circuit protection circuit 200,300 is simple in structure, and cost is lower.
Claims (10)
1. backlight open circuit protection circuit; comprise a plurality of backlight open-circuit testing circuits; one input circuit; one pulse-width modulator and a gauge tap; each backlight open-circuit testing circuit comprises that a backlight lamp tube and detects output terminal; this pulse-width modulator comprises a control end; whether be used to control this pulse-width modulator works; it is characterized in that: this input circuit comprises a plurality of diodes; a plurality of input resistances and a plurality of integrating capacitor; the negative pole of these a plurality of diodes is respectively via this integrating capacitor that is connected in parallel and this input resistance ground connection; the negative pole of these a plurality of diodes also is electrically connected to this a plurality of detection output terminals respectively; this gauge tap is connected between the positive pole and this control end of these a plurality of diodes, is used for the voltage according to this control end of Control of Voltage of these a plurality of diode cathodes.
2. backlight open circuit protection circuit as claimed in claim 1; it is characterized in that: this backlight open circuit protection circuit further comprises a capacitance; this gauge tap comprises a transistor and a current-limiting resistance; this transistorized grid is connected to a power supply via this current-limiting resistance; source electrode is connected to the positive pole of a plurality of diodes of this input circuit, and drain electrode is connected to this control end and via this capacitance ground connection.
3. backlight open circuit protection circuit as claimed in claim 2 is characterized in that: the resistance of this current-limiting resistance is 100K Ω, and this transistor is a N channel enhancement mos field effect transistor, and this power supply is a 5V direct supply.
4. backlight open circuit protection circuit as claimed in claim 3 is characterized in that: this 5V direct supply is provided by a pin of this pulse-width modulator.
5. backlight open circuit protection circuit as claimed in claim 1 is characterized in that: when this control end voltage was low-voltage, this pulse-width modulator quit work.
6. backlight open circuit protection circuit as claimed in claim 1; it is characterized in that: the resistance value of this input resistance is 1000K Ω; the capacitance of this integrating capacitor is 0.1 μ F, and this pulse-width modulator is that the employing model is the integrated circuit of OZ9910G, and the model of this diode is IN4148.
7. backlight open circuit protection circuit; comprise a plurality of backlight open-circuit testing circuits; one input circuit; one pulse-width modulator and a gauge tap; each backlight open-circuit testing circuit comprises that a backlight lamp tube and detects output terminal; this pulse-width modulator comprises a control end; whether be used to control this pulse-width modulator works; it is characterized in that: it comprises a plurality of diodes; a plurality of input resistances and a plurality of integrating capacitor; the negative pole of these a plurality of diodes is respectively via this integrating capacitor ground connection; the negative pole of these a plurality of diodes also is connected to this a plurality of detection output terminals via this input resistance respectively; this gauge tap is connected between the positive pole and this control end of these a plurality of diodes, is used for the voltage according to this control end of Control of Voltage of these a plurality of diode cathodes.
8. backlight open circuit protection circuit as claimed in claim 7; it is characterized in that: this backlight open circuit protection circuit further comprises a capacitance; this gauge tap comprises a transistor; this transistorized grid is connected to a power supply; source electrode is connected to the positive pole of a plurality of diodes of this input circuit, and drain electrode is connected to this control end and via this capacitance ground connection.
9. liquid crystal indicator as claimed in claim 8 is characterized in that: this gauge tap further comprises a current-limiting resistance, and this transistorized grid connects this power supply via this current-limiting resistance.
10. backlight open circuit protection circuit as claimed in claim 8 is characterized in that: this transistor is a N channel enhancement mos field effect transistor, and this transistorized forward voltage is 3V.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2007100774002A CN101399007B (en) | 2007-09-28 | 2007-09-28 | Backlight open-circuit protective circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2007100774002A CN101399007B (en) | 2007-09-28 | 2007-09-28 | Backlight open-circuit protective circuit |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN101399007A CN101399007A (en) | 2009-04-01 |
| CN101399007B true CN101399007B (en) | 2011-09-28 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN2007100774002A Expired - Fee Related CN101399007B (en) | 2007-09-28 | 2007-09-28 | Backlight open-circuit protective circuit |
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| Country | Link |
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| CN (1) | CN101399007B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103687259B (en) * | 2012-09-07 | 2015-12-30 | 神讯电脑(昆山)有限公司 | The protection circuit of inverter that fluorescent tube comes off |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5910709A (en) * | 1995-12-26 | 1999-06-08 | General Electric Company | Florescent lamp ballast control for zero -voltage switching operation over wide input voltage range and over voltage protection |
| US6118221A (en) * | 1997-10-16 | 2000-09-12 | Tokin Corporation | Cold-cathode tube lighting circuit with protection circuit for piezoelectric transformer |
| CN1881038A (en) * | 2005-06-17 | 2006-12-20 | 群康科技(深圳)有限公司 | Backlight open circuit protection circuit |
| CN1955790A (en) * | 2005-10-28 | 2007-05-02 | 群康科技(深圳)有限公司 | Backlight open-circuit protection circuit |
| CN1959476A (en) * | 2005-11-03 | 2007-05-09 | 群康科技(深圳)有限公司 | Backlihgt open circuit protection circuit |
| CN1980511A (en) * | 2005-12-01 | 2007-06-13 | 群康科技(深圳)有限公司 | Back-light open circuit protection circuit |
-
2007
- 2007-09-28 CN CN2007100774002A patent/CN101399007B/en not_active Expired - Fee Related
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5910709A (en) * | 1995-12-26 | 1999-06-08 | General Electric Company | Florescent lamp ballast control for zero -voltage switching operation over wide input voltage range and over voltage protection |
| US6118221A (en) * | 1997-10-16 | 2000-09-12 | Tokin Corporation | Cold-cathode tube lighting circuit with protection circuit for piezoelectric transformer |
| CN1881038A (en) * | 2005-06-17 | 2006-12-20 | 群康科技(深圳)有限公司 | Backlight open circuit protection circuit |
| CN1955790A (en) * | 2005-10-28 | 2007-05-02 | 群康科技(深圳)有限公司 | Backlight open-circuit protection circuit |
| CN1959476A (en) * | 2005-11-03 | 2007-05-09 | 群康科技(深圳)有限公司 | Backlihgt open circuit protection circuit |
| CN1980511A (en) * | 2005-12-01 | 2007-06-13 | 群康科技(深圳)有限公司 | Back-light open circuit protection circuit |
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| Publication number | Publication date |
|---|---|
| CN101399007A (en) | 2009-04-01 |
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Granted publication date: 20110928 Termination date: 20170928 |