CN100516992C - Backlight open circuit protection circuit - Google Patents
Backlight open circuit protection circuit Download PDFInfo
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- CN100516992C CN100516992C CNB2006100621958A CN200610062195A CN100516992C CN 100516992 C CN100516992 C CN 100516992C CN B2006100621958 A CNB2006100621958 A CN B2006100621958A CN 200610062195 A CN200610062195 A CN 200610062195A CN 100516992 C CN100516992 C CN 100516992C
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- backlight
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Abstract
The utility model relates to a backlight open protection circuit, comprising at least two backlight open detection circuits, a pulse-width modulation integrated circuit, a control switch and an input circuit. The backlight open detection circuit comprises a detection output. The input circuit comprises at least two first diodes, at least two input resistances, at least two first filtering capacitors, a first biasing resistor, a transistor and a peak detection circuit. The peak detection circuit comprises a second diode, a second filtering capacitor and a second biasing resistor. The cathode of the first diode is connected with the cathode of the second diode, and a circuit pitch point between the first diode and the second diode is connected with a power supply through the biasing resistor. Each anode of the second diode is connected with a detection output after connecting in series with an input resistance. The anode of the second diode is connected with the grid of the transistor, and is respectively put to earth through the second filtering capacitor and the second biasing resistor. The source cathode of the transistor is put to earth. The drain of the transistor is connected with the pulse-width modulation integrated circuit through the control switch.
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
Because it is frivolous that LCD has, power consumption is hanged down and characteristics such as radiation is few, therefore is widely used in fields such as portable DVD player, visual music player, mobile phone and notebook computer.Because the liquid crystal molecule itself in the LCD is not luminous; therefore LCD need show by the luminous image of realizing of a module backlight; common module backlight comprises the pulse-width modulation integrated circuit of a plurality of backlight lamp tubes and these a plurality of backlight lamp tube working currents of adjusting; when a backlight lamp tube job occurs unexpected; when causing the output load open circuit of this pulse-width modulation integrated circuit, this pulse-width modulation integrated circuit needs a backlight open circuit protection circuit that it is quit work.
Please refer to Fig. 1, is a kind of synoptic 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 modulation integrated circuit 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 connected to the source electrode of this transistor seconds 1332, the drain electrode of this transistor seconds 1332 is connected to the source electrode of the 3rd transistor 1333, the drain electrode of the 3rd transistor 1333 is 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 pole 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 syndeton of this transistor seconds 1332, the 3rd transistor 1333 and the 4th transistor 1334 is connected identical with the grid of this first transistor 1331.The positive pole of these four diodes 131 is respectively as four input ends of this input circuit 130, and is connected respectively to and detects output terminal 112.
This pulse-width modulation integrated circuit 150 comprises a current sample end 151, and when this current sample end 151 was drawn to low-voltage, this pulse-width modulation integrated circuit 150 quit 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 connected to the grid of current sample end 151, the five transistors 171 of this pulse-width modulation integrated circuit 150 and the drain electrode of the 4th transistor 1334 all is connected to a 5V power supply (pin of pulse-width modulation integrated circuit 150) via this current-limiting resistance 172.
During operate as normal, four of these four testing circuits 110 are detected output terminal 112 voltages four high voltage signals of output signal respectively.These four high voltage signals make this first transistor 1331, transistor seconds 1332, the 3rd transistor 1333 and the 4th transistor 1334 all open 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.
When any testing circuit 110 detects backlight lamp tube 111 for open circuit or shorted to earth, the detection output terminal 112 of this testing circuit 110 produces a low voltage signal, this low voltage signal makes this make one of this first transistor 1331, transistor seconds 1332, the 3rd transistor 1333 and the 4th transistor 1334 close by this diode 131, because the drain electrode of the grid of the 5th transistor 171 and the 4th transistor 1334 all is connected to a power supply via this current-limiting resistance 172.Therefore the grid of the 5th transistor 171 is a high voltage; the 5th transistor 171 is opened; so this current sample end 151 that connects with the drain electrode of the 5th transistor 171 is drawn to be low-voltage, this pulse-width modulation integrated circuit 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
In order to solve the complicated shortcoming of prior art backlight open circuit protection circuit structure, be necessary to provide a kind of backlight open circuit protection circuit simple in structure.
A kind of backlight open circuit protection circuit, it comprises at least two backlight open detection circuit, a pulse-width modulation integrated circuit, a gauge tap and an input circuit.This backlight open detection circuit comprises that a backlight lamp tube and detects output terminal.This pulse-width modulation integrated circuit comprises a current sample end, and when this current sample end was drawn to low-voltage, this pulse-width modulation integrated circuit quit work.This gauge tap comprises a first transistor.This input circuit comprises at least two first diodes, at least two input resistances, at least two first filter capacitors, one first biasing resistor, a transistor seconds and peak-detector circuits.This peak-detector circuit comprises one second diode, one second filter capacitor and one second biasing resistor.The source ground of this first transistor, the drain electrode of this first transistor are connected to the current sample end of this pulse-width modulation integrated circuit, and the grid of this first transistor is connected to a power supply.The positive pole of this first diode is connected to the positive pole of this second diode, and the circuit node between first diode and this second diode is connected to this power supply via this biasing resistor.The negative pole of each diode is connected respectively and is connected to one behind the input resistance and detects output terminal.The negative pole of this second diode is connected to the grid of this transistor seconds, and respectively via this second filter capacitor and the second biasing resistor ground connection.The source ground of this transistor seconds.The drain electrode of this transistor seconds is connected to the grid of this first transistor.
Compared to prior art, the input circuit in the above-mentioned backlight open circuit protection circuit only comprises a transistor.And, do not need to increase transistor even increase this backlight open circuit protection circuit of backlight lamp tube yet.Therefore, this backlight open circuit protection circuit is simple in structure, and cost is lower.
Description of drawings
Fig. 1 is a kind of circuit diagram of prior art backlight open circuit protection circuit.
Fig. 2 is the synoptic diagram of backlight open circuit protection circuit one better embodiment of the present invention.
Embodiment
Please refer to Fig. 2, is the synoptic diagram of the disclosed a kind of backlight open circuit protection circuit 200 of the present invention's one better embodiment.This backlight open circuit protection circuit 200 comprises a plurality of backlight open detection circuit 210, an input circuit 230, a pulse-width modulation integrated circuit 250 and a gauge tap 270.
Each backlight open detection circuit 210 comprises that a backlight lamp tube 211 and detects output terminal 212.
This pulse-width modulation integrated circuit 250 comprises a current sample end 251, and when this current sample end 251 was drawn to low-voltage, this pulse-width modulation integrated circuit 250 quit work.
This gauge tap 270 comprises a first transistor 271 and a current-limiting resistance 272, the source ground of this first transistor 271, the drain electrode of this first transistor 271 is connected to the current sample end 251 of this pulse-width modulation integrated circuit 250, the grid of this first transistor 271 is connected to a 5V direct supply via this current-limiting resistance 272, and this 5V direct supply is provided by a pin of this pulse-width modulation integrated circuit 250.
This input circuit 230 comprises a plurality of first diodes 231, a plurality of input resistance 232, a plurality of first filter capacitor 233, one first biasing resistor 234, a transistor seconds 235, a charging capacitor 239 and a peak-detector circuit 290.This peak-detector circuit 290 comprises one second diode 236, one second filter capacitor 237 and one second biasing resistor 238.
The positive pole of these a plurality of first diodes 231 all is connected to the positive pole of this second diode 236, and the circuit node between first diode 231 and this second diode 236 is connected to this 5V direct supply via this biasing resistor 234.The negative pole of these a plurality of first diodes 231 is respectively via these first filter capacitor, 233 ground connection, and the negative pole of these a plurality of first diodes 231 a plurality of input ends of an input resistance 232 backs as this input circuit 230 of connecting respectively.Each input end of this input circuit 230 is connected to one and detects output terminal 212.The negative pole of this second diode 236 is connected to the grid of this transistor seconds 235, and respectively via this second filter capacitor 237 and second biasing resistor, 238 ground connection.The source ground of this transistor seconds 235.The drain electrode of this transistor seconds 235 is output terminals of this input circuit 230, and it is connected to the grid of this first transistor 271 and via these charging capacitor 239 ground connection.This charging capacitor 239 is used to reduce the moment firing current of this first transistor 271.
It is the diode of SN4148 that this first diode 231 and diode 236 all adopt model.The resistance value of this current-limiting resistance 272, this input resistance 232, this first biasing resistor 234 and this second biasing resistor 238 is respectively 180K Ω, 10K Ω, 100K Ω, 470K Ω.The capacitance of this first filter capacitor 233 and second filter capacitor 237 is all 0.1 μ F.This first transistor 271 and transistor seconds 235 all be N type channel depletion mode metal oxide semiconductcor field effect transistor (N-Channel depletion modeMetal-Oxide-Semiconductor Field-Effect Transistor, N-MOSFET) or other alternative npn type bipolar transistor.This pulse-width modulation integrated circuit 250 is that the employing model is the integrated circuit of OZ9910G.This backlight lamp tube 211 be cathode fluorescent tube (Cold Cathode Fluorescent Light, CCFL).
During operate as normal, the first 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 first fluorescent tube sample rate current becomes the dc high voltage of an about 3V after via this input resistance 232 and these first filter capacitor, 233 integrations.This diode 231 is 3.7V with this 3V dc high voltage lifting then, and is transferred to this transistor seconds 235 via this peak-detector circuit 290, makes this transistor seconds 235 conductings.Then the grid of this first transistor 271 is via these transistor seconds 235 ground connection of conducting, by drop-down be low-voltage, so this first transistor 271 is closed.These pulse-width modulation integrated circuit 250 operate as normal.
When any backlight open detection circuit 210 detects backlight lamp tube 211 for open circuit or shorted to earth, the second less fluorescent tube sample rate current of detection output terminal 212 output one amplitudes of this backlight open detection circuit 210.This second fluorescent tube sample rate current becomes a DC voltage less than 2V after via this input resistance 232 and these first filter capacitor, 233 integrations.Should be less than the DC voltage of 2V via these diode 231 liftings, via being a low-voltage behind these peak-detector circuit 290 peak detections, it is not enough so that these transistor seconds 235 conductings then.Because the grid of this first transistor 271 is connected to this 5V direct supply; this 5V direct supply makes this first transistor 271 open; so being connected to this current sample end 251 in 271 drain electrodes of this first transistor is drawn and is low-voltage; this pulse-width modulation integrated circuit 250 quits work, and realizes the backlight open-circuit defencive function.
Compared to prior art, the input circuit 230 in this backlight open circuit protection circuit 200 only comprises a transistor 235, even and increase backlight lamp tube 211, the input circuit 230 in this backlight open circuit protection circuit 200 does not need to increase number of transistors yet.Therefore, this backlight open circuit protection circuit 200 is simple in structure, and cost is lower.
Claims (10)
1. backlight open circuit protection circuit comprises:
At least two backlight open detection circuit, each backlight open detection circuit comprise that a backlight lamp tube and detects output terminal;
One pulse-width modulation integrated circuit, it comprises a current sample end, when this current sample end was drawn to low-voltage, this pulse-width modulation integrated circuit quit work;
One gauge tap, this gauge tap comprises a first transistor, the source ground of this first transistor, drain electrode is connected to the current sample end of this pulse-width modulation integrated circuit, and grid is connected to a power supply;
One input circuit;
It is characterized in that: this input circuit comprises:
At least two first diodes;
At least two input resistances;
At least two first filter capacitors;
One first biasing resistor;
One transistor seconds; With
One peak-detector circuit, it comprises one second diode, one second filter capacitor and one second biasing resistor;
The positive pole of this first diode is connected to the positive pole of this second diode, and the circuit node between first diode and this second diode is connected to this power supply via this first biasing resistor, the negative pole of each first diode is via this first filter capacitor ground connection, and the negative pole of each first diode is connected respectively and is connected to one behind the input resistance and detects output terminal, the negative pole of this second diode is connected to the grid of this transistor seconds, and respectively via this second filter capacitor and the second biasing resistor ground connection, the source ground of this transistor seconds, the drain electrode of this transistor seconds is connected to the grid of this first transistor.
2. backlight open circuit protection circuit as claimed in claim 1 is characterized in that: this backlight open circuit protection circuit further comprises a current-limiting resistance, and the grid of this first transistor is connected to this power supply via this current-limiting resistance.
3. backlight open circuit protection circuit as claimed in claim 2 is characterized in that: the resistance value of this current-limiting resistance is 180K Ω.
4. backlight open circuit protection circuit as claimed in claim 1 is characterized in that: this first and second transistor is a N type channel depletion mode metal oxide semiconductcor field effect transistor.
5. backlight open circuit protection circuit as claimed in claim 1 is characterized in that: this first and second transistor is a npn type bipolar transistor.
6. backlight open circuit protection circuit as claimed in claim 1 is characterized in that: the resistance value of this input resistance, first biasing resistor and second biasing resistor is respectively 10K Ω, 100K Ω, 470K Ω.
7. backlight open circuit protection circuit as claimed in claim 1 is characterized in that: the capacitance of this first filter capacitor and second filter capacitor is all 0.1 μ F.
8. backlight open circuit protection circuit as claimed in claim 1 is characterized in that: this backlight open circuit protection circuit further comprises a charging capacitor, and the drain electrode of this transistor seconds is via this charging capacitor ground connection.
9. backlight open circuit protection circuit as claimed in claim 1 is characterized in that: this power supply is a 5V direct supply.
10. backlight open circuit protection circuit as claimed in claim 1 is characterized in that: this backlight lamp tube is a cathode fluorescent tube.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB2006100621958A CN100516992C (en) | 2006-08-18 | 2006-08-18 | Backlight open circuit protection circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB2006100621958A CN100516992C (en) | 2006-08-18 | 2006-08-18 | Backlight open circuit protection circuit |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN101126847A CN101126847A (en) | 2008-02-20 |
| CN100516992C true CN100516992C (en) | 2009-07-22 |
Family
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNB2006100621958A Expired - Fee Related CN100516992C (en) | 2006-08-18 | 2006-08-18 | Backlight open circuit protection circuit |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN100516992C (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TWI722391B (en) * | 2019-02-26 | 2021-03-21 | 瑞鼎科技股份有限公司 | Light-emitting diode display panel testing device and light-emitting diode display panel testing method |
-
2006
- 2006-08-18 CN CNB2006100621958A patent/CN100516992C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CN101126847A (en) | 2008-02-20 |
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Granted publication date: 20090722 Termination date: 20190818 |
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| CF01 | Termination of patent right due to non-payment of annual fee |