CN101247042A - Video protection circuit - Google Patents
Video protection circuit Download PDFInfo
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- CN101247042A CN101247042A CNA2007100672579A CN200710067257A CN101247042A CN 101247042 A CN101247042 A CN 101247042A CN A2007100672579 A CNA2007100672579 A CN A2007100672579A CN 200710067257 A CN200710067257 A CN 200710067257A CN 101247042 A CN101247042 A CN 101247042A
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Abstract
The present invention discloses a video protecting circuit. Through the adopting of a thermistor, a resistor, an air discharge tube, a capacitance and a diode, the two-stage protection and four-time energy attenuation and absorption are formed. The damping energy are effectively graded and the damage of the energy impulse to the back stage circuit is reduced; and the damage of lightning stroke, commercial electric power leakage and static to the equipment can be prevented simultaneously. At the same time the video quality is not affected; besides, the invention has the characters of low cost and easy realization.
Description
Technical field
The present invention relates to the video protection technology, especially, relate to a kind of high-energy electric current, the voltage signal that seal on the video signal cable can decay and bypass protection, make it not damage equipment, with the video protection circuit of protection equipment operate as normal.
Background technology
At present, the known camera video output exchange waies that adopt more, promptly signal level with reference to fluctuate, this circuit is to capacitance-sensitive, and there are parasitic capacitance over the ground in back end signal line and device, promptly forms the capacitance partial pressure phase modulation, the normal phase place and the amplitude of jammer signal, and then influence image quality.
In existing video signal protection design; mostly be to adopt the TVS pipe to realize; because the physical structure of TVS pipe; parasitic electric capacity reaches tens of PF to hundred PF usually on the TVS pipe PN junction; junction capacitance has the effect of bypass to video, and the high fdrequency component of attenuation video signal descends image definition; the edge has a common boundary fuzzy, the loss video signal quality.
The video protection object is divided two kinds at present:
1, static
Be characterized in static transient voltage height, the time is fast.Limited resource-power, response time, junction capacitance.Response time requires the TVS junction capacitance more little more soon, and the junction capacitance small-power is just limited, and the transient voltage height that forms at the TVS two ends is restricted the effect of TVS pipe.
2, thunderbolt pulse and civil power electric leakage
Be characterized in that energy is big, longer duration.Limited resource--TVS power, junction capacitance.The big more response time that power is done is slow more, and junction capacitance is big more, and is just serious more to the video influence.The effect of TVS pipe is restricted.
Summary of the invention
The objective of the invention is to provides a kind of video protection circuit at the existing vision signal deficiency responsive simultaneously to electric capacity, voltage, electric current; This video protection circuit can protect the macro-energy high voltage, and avoids the influence of protective device to video signal quality, reaches the purpose of protection late-class circuit trouble free service.
The technical solution adopted in the present invention is: a kind of video protection circuit, and it mainly is made up of thermistor R1, resistance R 2, air discharge tube TED1, capacitor C 1, diode D1 and diode D2; Wherein, thermistor R1 one end links to each other with resistance R 2, air discharge tube TED1 and capacitor C 1 respectively, the other end of the other end of resistance R 2 and air discharge tube TED1 is ground connection all, the other end of capacitor C 1 links to each other with the negative electrode of diode D1, the anode of diode D2 respectively, the anode of diode D1 links to each other with power supply, the minus earth of diode D2.
Further, the resistance of described thermistor R1 is 20-25 ohm, and the resistance of resistance R 2 is 50-55 ohm, and the voltage of air discharge tube TED1 is 63-77V, and the appearance value of capacitor C 1 is 2.2-3.3uF, and diode D1 and diode D2 are the speed-sensitive switch diode.
The invention has the beneficial effects as follows: the present invention adopts thermistor, resistance, air discharge tube, electric capacity, diode, forms two-stage protection and four energy attenuatioies, absorption, and the classification damping capacity reduces the destruction of energy pulse to late-class circuit effectively; Can accomplish to protect thunderbolt, civil power electric leakage, static destruction simultaneously, not influence video quality simultaneously equipment; In addition, the present invention also has with low cost, realizes characteristic of simple.
Description of drawings
Describe the present invention in detail below in conjunction with the drawings and specific embodiments, it is more obvious that purpose of the present invention and effect will become.
Fig. 1 is the schematic diagram of video protection circuit of the present invention;
Fig. 2 is the application exemplary plot of video protection circuit of the present invention.
Embodiment
As shown in Figure 1, video protection circuit of the present invention mainly is made up of thermistor R1, resistance R 2, air discharge tube TED1, capacitor C 1, diode D1 and diode D2; Thermistor R1 one end links to each other with the video input signals line, the other end links to each other with resistance R 2, air discharge tube TED1 and capacitor C 1 respectively, the other end ground connection of resistance R 2, the other end ground connection of air discharge tube TED1, the other end of capacitor C 1 links to each other with the video output signals line with the negative electrode of diode D1, the anode of diode D2 respectively, the anode of diode D1 links to each other with power supply, the minus earth of diode D2.
The resistance of thermistor R1 is 20-25 ohm, the resistance of resistance R 2 is 50-55 ohm, and the voltage of air discharge tube TED1 is 63-77V, and the appearance value of capacitor C 1 is 2.2-3.3uF, diode D1 and diode D2 can adopt the speed-sensitive switch diode, as 1N4148, BAV99.
As shown in Figure 2, the vision signal of video camera output arrives ground through thermistor R1 and resistance R 2.On the node of thermistor R1, resistance R 2, connect air discharge tube TED1 to ground.Be connected capacitor C 1 on the node of thermistor R1, resistance R 2 and air discharge tube TED1, the other end of capacitor C 1 is connected to the pin input of video a/d device chip.On the node that the pin of capacitor C 1, video a/d device chip is imported, connect the positive level of power supply, by diode D2 ground connection by diode D1.
The present invention absorbs classification damping capacity effectively by two-stage protection and four energy attenuatioies, reduces the destruction of energy pulse to late-class circuit.Make equipment be in the works fine state, improve the reliability of product.
First order protection is made up of thermistor R1, resistance R 2 and air discharge tube TED1.Thermistor R1 constitutes energy attenuation for the first time, absorption, and thermistor R1 utilizes resistance increase principle under the over-current state, and the electric current that flows through thermistor is reduced, and reaches the purpose of damping capacity.Air discharge tube TED1 constitutes the second energy decay, absorbs, and air discharge tube TED1 utilizes the mode leakage current of ionization device inside blanketing gas, and the energy that is higher than ionization voltage is released by the breakdown device internal gas, reaches the purpose of damping capacity.
Second level protection is made up of capacitor C 1, diode D1 and diode D2.C1 plays the effect of coupling vision signal in circuit, the capacitive reactance of C1 is a finite value simultaneously, part energy can decay, reach the purpose of energy attenuation for the third time, D1 releases the direct impulse energy to electric power loop, D2 releases the negative-going pulse energy to earth-return, reach the purpose of the 4th energy attenuation.
Under normal mode of operation, as shown in Figure 1, in the video line video incoming line, normal vision signal to ground, is finished the video properties impedance matching by thermistor R1, resistance R 2.The action threshold values of air discharge tube TED1 is far above the standard video source voltage amplitude, and air discharge tube TED1 is failure to actuate.The two poles of the earth of TED1 distance physically are far, and the junction capacitance of formation is very little, and numerical value does not impact video below the pF level.C1 coupling video signal stops the DC component in the video simultaneously, and the video output network fixes on the current potential pincers on 0 level by IC (video a/d) is inner, is convenient to the inner mould/number conversion of IC (video a/d).Diode D1 and diode D2 fix on the current potential pincers on 0 level owing to IC (video a/d) is inner, balance out the video source end and produce parasitic capacitance dividing potential drop phase modulation effect because of capacitively coupled output, the junction capacitance of D1 and D2 is about number PF, so the junction capacitance of D1 D2 in parallel does not influence video quality.
Under the non-normal working pattern, heavy current/voltage is coupled into video line video incoming line, arrives ground by thermistor R1, resistance R 2 earlier, finishes the impedance matching of video.Heavy current/voltage is far above the action threshold values of TED1, and air discharge tube TED1 moves, and the energy that is higher than threshold values is absorbed by air discharge tube TED1 rapidly.And thermistor R1 have macro-energy by the time can generate heat, resistance rises rapidly, the energy (electric current) of thermistor R1 is flow through in decay, is lower than the coupling of the energy of TED1 threshold values by capacitor C 1, enters the video output network.Direct impulse is discharged into energy on the power supply VCC by the response of diode D1, clamps in the scope of the forward conduction voltage sum that fixes on VCC and diode, finishes the charging process to capacitor C 1, and according to capacitance characteristic, the direct current electric charge is to penetrate capacitor C 1.In like manner negative-going pulse is by diode D2, accumulation on the capacitor C 1 congratulated by sending a telegram on be discharged into ground, the negative sense level clamped fix in the forward conduction voltage range of diode, guarantees the operate as normal of IC (video a/d).
The foregoing description is used for the present invention that explains, rather than limits the invention, and in the protection range of spirit of the present invention and claim, any modification and change to the present invention makes all fall into protection scope of the present invention.
Claims (2)
1. a video protection circuit is characterized in that, it mainly is made up of thermistor R1, resistance R 2, air discharge tube TED1, capacitor C 1, diode D1 and diode D2.Wherein, thermistor R1 one end links to each other with resistance R 2, air discharge tube TED1 and capacitor C 1 respectively, the other end of the other end of resistance R 2 and air discharge tube TED1 is ground connection all, the other end of capacitor C 1 links to each other with the negative electrode of diode D1, the anode of diode D2 respectively, the anode of diode D1 links to each other with power supply, the minus earth of diode D2.
2. circuit according to claim 1, it is characterized in that, the resistance of described thermistor R1 is 20-25 ohm, the resistance of resistance R 2 is 50-55 ohm, the voltage of air discharge tube TED1 is 63-77V, the appearance value of capacitor C 1 is 2.2-3.3uF, and diode D1 and diode D2 are the speed-sensitive switch diode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNA2007100672579A CN101247042A (en) | 2007-02-14 | 2007-02-14 | Video protection circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNA2007100672579A CN101247042A (en) | 2007-02-14 | 2007-02-14 | Video protection circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN101247042A true CN101247042A (en) | 2008-08-20 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CNA2007100672579A Pending CN101247042A (en) | 2007-02-14 | 2007-02-14 | Video protection circuit |
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| CN (1) | CN101247042A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102185304A (en) * | 2011-05-16 | 2011-09-14 | 浙江大华技术股份有限公司 | Surge protection circuit of video input signal |
-
2007
- 2007-02-14 CN CNA2007100672579A patent/CN101247042A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102185304A (en) * | 2011-05-16 | 2011-09-14 | 浙江大华技术股份有限公司 | Surge protection circuit of video input signal |
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Open date: 20080820 |