CN203225705U - Input protective circuit - Google Patents
Input protective circuit Download PDFInfo
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- CN203225705U CN203225705U CN 201320046525 CN201320046525U CN203225705U CN 203225705 U CN203225705 U CN 203225705U CN 201320046525 CN201320046525 CN 201320046525 CN 201320046525 U CN201320046525 U CN 201320046525U CN 203225705 U CN203225705 U CN 203225705U
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- circuit
- voltage
- input
- protective circuit
- preamplifier
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Abstract
The utility model discloses an input protective circuit for protecting an NMR preamplifier from effects of inputting large signals. The input protective circuit is connected between an input port and a subsequent preamplifier and comprises two stages of protective circuits. A first protective circuit consists of crossed diodes. When input signals are higher than an operation scope, the diodes are conducted, and current shunts by the diodes and cannot flow in the subsequent preamplifier. A second protective circuit consists of a resistor, a capacitor, a voltage stabilizing diode, a voltage comparator and a MOS transistor. Conduction and cut-off states of the MOS transistor are controlled by outputting high and low level signals through the voltage comparator. When the input signals are higher than an operation scope, the MOS transistor is cut off and the input signals cannot enter in the subsequent preamplifier. The two stages of circuits protect the NMR preamplifier from interference of inputting the large signals.
Description
Technical field
The utility model relates to a kind of input protection circuit, relates in particular to a kind of circuit of avoiding importing the large-signal influence for the protection of the nulcear magnetic resonance (NMR) preamplifier.
Background technology
Usually, the nulcear magnetic resonance (NMR) preamplifier can be subjected to importing the interference of large-signal and cisco unity malfunction, and the signal significantly of moment input can form whole system and disturb even damage circuit.This protective circuit adopts the in parallel or series connection formation of general-purpose diode usually, and it is connected between input signal and the subsequent conditioning circuit, though simple and practical, reliability is poor.Shortcoming one is that general-purpose diode exists certain response time, and when diode failed in time to respond, the input large-signal entered follow-up preamplifier and will damage circuit board.Shortcoming two is methods that protective circuit of diode adopts the electric current shunting, when input signal far exceeds working range, still has big current signal to enter follow-up preamplifier.
Summary of the invention
Therefore, the utility model is applied to solving and has the problems referred to above of the prior art, and the purpose of this utility model provides and a kind ofly avoids importing the influence of large-signal and a kind of input protection circuit of designing for the protection of the nulcear magnetic resonance (NMR) preamplifier.
Basic design of the present utility model is that input signal forms interference to whole system to the design dual-electrode protecting circuit to overcome significantly.
First protective circuit, it is connected between input port and the second protective circuit input, is used for when input signal is higher than working range, flows to ground by the input current that allows input signal, protects preamplifier; And
Second protective circuit; it is connected between the first protective circuit output and the nulcear magnetic resonance (NMR) preamplifier input; be used for when first protective circuit can not be shunted input signal fully, by disconnecting the path between input signal and the preamplifier, protecting preamplifier.
Further, first protective circuit comprises that at least 2 are connected in parallel to each other and diode that current polarity is opposite.
Further, second protective circuit is made up of voltage comparator circuit and switching circuit; Voltage comparator circuit is to be made of resistance, electric capacity, general-purpose diode, voltage stabilizing didoe, voltage comparator; Switching circuit is made of MOS transistor and resistance.
Characteristics of the present utility model are that first protective circuit utilizes crossed diodes to the shunting of input large-signal; second protective circuit is utilized voltage comparator control MOS transistor; when input signal exceeded working range, MOS transistor disconnected, and input signal can not enter follow-up preamplifier.
As mentioned above, the utility model forms duplicate protection by dual-electrode protecting circuit to follow-up internal circuit, and circuit is simple, reliable.
How further specify goal of the invention of the present utility model below in conjunction with accompanying drawing realizes:
Description of drawings
Fig. 1 shows and is suitable for a kind of traditional protective circuit of the present utility model.
Fig. 2 shows the first protective circuit structure of the present utility model.
Fig. 3 shows the second protective circuit structure of the present utility model.
Fig. 4 shows the utility model protective circuit structure.
Embodiment
Fig. 1 shows and is suitable for a kind of traditional input protection circuit of the present utility model.As shown in the figure, 101 is the crossed diodes protective circuit in this protective circuit, and 102 is shielded electronic device.
Fig. 2 shows the structure according to first protective circuit of the input protection circuit of the utility model embodiment.
By reference to the accompanying drawings 2 as can be seen first protective circuit comprise four diode D1, D2, D3, D4.D1 and D2, D3 and D4 form two groups of crossed diodes respectively among Fig. 2.Crossed diodes refers to be connected in parallel to each other and has the diode of opposite polarity.In the design of the present utility model, first protective circuit comprises that at least 2 are connected in parallel to each other and diode that current polarity is opposite.
Diode is a kind of electronic device with unilateal conduction characteristic.During forward bias, diode current flow, electric current is by diode, and during reverse bias, diode ends, and the blocking-up electric current passes through diode.Usually, diode has certain cut-in voltage when forward bias, and is that the cut-in voltage of a plurality of diodes that first protective circuit of the present utility model adopts can be identical or different.
When input voltage during greater than the diode cut-in voltage, diode current flow, otherwise diode ends.In the utility model; the operating characteristic of first protective circuit is: when the voltage in the working range (input voltage is less than the diode cut-in voltage) passes through first protective circuit; diode ends; electric current flows into second protective circuit; when the voltage that is higher than working range (input voltage is greater than the diode cut-in voltage) passes through this first protective circuit; diode current flow, electric current is shunted rapidly by diode.
Diode can be regarded an ideal diode and a resistance series connection as; an aspect that limits the first protective circuit ability is that diode has series resistance; series impedance is more high, and diode shunting ability is more weak, and more electric current will be by follow-up preamplifier.
A plurality of diodes compose in parallel the diode series resistance that first protective circuit can reduce entire circuit, and four diodes such as D1, D2, D3, D4 are connected in parallel to each other among Fig. 2, can reduce series resistance.Like this, most electric current will pass through diode circuit.
In addition, the diode of the utility model employing has the response time fast.Ideally, the response time is less than 10ns, shunts fast when being higher than the diode cut-in voltage at input signal.
Fig. 3 has gone out the structure according to second protection circuit of the input protection circuit of the utility model embodiment.By voltage comparator circuit 301,302 and switching circuit 303 form.In the design of the present utility model, second protective circuit is made up of voltage comparator circuit and switching circuit, and voltage comparator circuit is to be made of resistance, electric capacity, general-purpose diode, voltage stabilizing didoe, voltage comparator, and switching circuit is made of MOS transistor and resistance.
Voltage comparator 7 in-phase input ends 302 according to the present embodiment shown in Fig. 3 comprise: after resistance 5 and resistance 6 series connection, one end connection-5V power supply, other end ground connection is for voltage comparator provides reference voltage, electric capacity 10 is connected in parallel on resistance 5 two ends, the pulse of filtering High-frequency Interference.
Voltage comparator 7 inverting inputs 301 according to the present embodiment shown in Fig. 3 comprise: diode 1, resistance 2, voltage stabilizing didoe 3, resistance 4, electric capacity 8, electric capacity 9.
Voltage comparator has in-phase end and end of oppisite phase, and wherein, in-phase end comprises that two resistance that are one another in series are used for providing reference potential.
Voltage stabilizing didoe 3 is a kind of very high-resistance diodes that all have before critical reverse breakdown voltage, and during reverse breakdown, in certain current range, terminal voltage is almost constant.It is the voltage-stabiliser tube of 3.3V that the utility model voltage comparator circuit adopts the voltage stabilizing value.
Voltage stabilizing didoe 3 comprises anode and negative electrode, and diode 1 links to each other with the negative electrode of voltage-stabiliser tube 3 with the node of resistance 2, and the anode of voltage-stabiliser tube 3 is connected with the reverse input end (-) of voltage comparator 7.Resistance 4 one ends are connected with the positive pole of voltage-stabiliser tube 3, and the other end is connected with power supply, and resistance 4 is used to the anode of voltage-stabiliser tube 3 that terminal voltage is provided, and electric capacity 8, electric capacity 9 are in parallel with resistance 2, voltage-stabiliser tube 3 respectively, and it is used for the High-frequency Interference pulse of filtering input signal.
In the design of the present utility model, voltage stabilizing didoe 3 comprises anode and negative electrode, and anode links to each other with the voltage comparator end of oppisite phase, and negative electrode links to each other with node between diode 1 and the resistance 2; Resistance 4 is used for providing voltage stabilizing didoe 3 anode tap voltages.
Switching circuit 303 according to the present embodiment shown in Fig. 3 is made up of resistance 11 and MOS transistor 12.
The operating characteristic of second protective circuit is: when the voltage in the working range passed through described voltage comparator circuit, voltage comparator input terminal voltage was in the same way exported high level signal greater than reverse input end; Voltage in being higher than working range when this voltage comparator circuit, voltage comparator in the same way input terminal voltage less than reverse input end, the output low level signal; With
Switching circuit, conducting when above-mentioned voltage comparator circuit is exported above-mentioned high level signal makes more multiple current by described preamplifier, ends when above-mentioned comparison circuit is exported above-mentioned low level signal, disconnects the path between input signal and the preamplifier.
Fig. 4 shows the input protection circuit according to the utility model embodiment, comprises first protective circuit 401 and second protective circuit 402.
The voltage comparator that the utility model adopts is AD8561, the power supply of employing-5V power supply.
According to the utility model shown in Figure 4 second protective circuit structure, voltage comparator in-phase input end (+) reference voltage is V
(+)Be about-2.2V.
Input signal is during less than diode 1 cut-in voltage, and diode 1 ends, and the negative electrode of voltage stabilizing didoe 3 and the terminal voltage between the anode are less than 3.3V, and voltage-stabiliser tube ends, voltage comparator inverting input voltage V
(-)Less than in-phase input end voltage V
(+), voltage comparator output high level signal.
When input signal is higher than diode 1 cut-in voltage, diode 1 conducting, the negative electrode of voltage-stabiliser tube 3 and the voltage between the anode is greater than 3.3V, the voltage-stabiliser tube conducting, voltage comparator end of oppisite phase voltage is greater than in-phase end voltage, voltage comparator output low level signal.
Voltage comparator output low level signal, MOS transistor 12 grid voltages are low level, disconnect between the source class S of MOS transistor 12 and the drain D, input signal can not enter follow-up preamplifier.
Claims (8)
1. an input protection circuit is characterized in that, is connected between input port and the nulcear magnetic resonance (NMR) preamplifier, comprising:
First protective circuit, it is connected between input port and the second protective circuit input, is used for when described input signal is higher than working range, flows to ground by the input current that allows described input signal, protects described preamplifier; And
Second protective circuit; it is connected between the first protective circuit output and the nulcear magnetic resonance (NMR) preamplifier input; described first protective circuit is used for when can not be shunted described input signal fully; by disconnecting the path between described input signal and the described preamplifier, protect described preamplifier.
2. according to the described input protection circuit of claim 1, wherein, described first protective circuit comprises that at least 2 are connected in parallel to each other and diode that current polarity is opposite.
3. according to the described input protection circuit of claim 1, wherein, the operating characteristic of described first protective circuit is: when the voltage in the working range during by described first protective circuit, diode ends, and electric current flows into described second protective circuit; When the voltage that is higher than working range passes through this first protective circuit, diode current flow, electric current is shunted rapidly by diode.
4. according to the described input protection circuit of claim 1, wherein, described second protective circuit is made up of voltage comparator circuit and switching circuit; Voltage comparator circuit is to be made of resistance, electric capacity, general-purpose diode, voltage stabilizing didoe, voltage comparator; Switching circuit is made of MOS transistor and resistance.
5. according to the described input protection circuit of claim 4, wherein, voltage comparator has in-phase end and end of oppisite phase, and wherein, this in-phase end comprises that two resistance that are one another in series are used for providing reference potential.
6. according to the described input protection circuit of claim 4, wherein, described voltage stabilizing didoe (3) comprises anode and negative electrode, and described anode links to each other with the voltage comparator end of oppisite phase, and described negative electrode links to each other with node between diode (1) and the resistance (2); Resistance (4) is used for providing voltage stabilizing didoe (3) anode tap voltage.
7. according to the described input protection circuit of claim 4, wherein, the grid of described MOS transistor is connected with the voltage comparator output, and source electrode is connected with the described first protective circuit output, and drain electrode connects described preamplifier.
8. according to the described input protection circuit of claim 4, wherein, the operating characteristic of described second protective circuit is: when the voltage in the working range passed through described voltage comparator circuit, voltage comparator input terminal voltage was in the same way exported high level signal greater than reverse input end; Voltage in being higher than working range when this voltage comparator circuit, voltage comparator in the same way input terminal voltage less than reverse input end, the output low level signal; With
Switching circuit, conducting when above-mentioned voltage comparator circuit is exported above-mentioned high level signal makes more multiple current by described preamplifier, ends when above-mentioned comparison circuit is exported above-mentioned low level signal, disconnects the path between input signal and the preamplifier.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 201320046525 CN203225705U (en) | 2013-01-28 | 2013-01-28 | Input protective circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 201320046525 CN203225705U (en) | 2013-01-28 | 2013-01-28 | Input protective circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN203225705U true CN203225705U (en) | 2013-10-02 |
Family
ID=49252695
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 201320046525 Expired - Fee Related CN203225705U (en) | 2013-01-28 | 2013-01-28 | Input protective circuit |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN203225705U (en) |
-
2013
- 2013-01-28 CN CN 201320046525 patent/CN203225705U/en not_active Expired - Fee Related
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C14 | Grant of patent or utility model | ||
| GR01 | Patent grant | ||
| C17 | Cessation of patent right | ||
| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20131002 Termination date: 20140128 |