How does common protection circuit affect electric current to detect the precision of amplifier
[introduction] harsh environment is the reality that a lot of electrical system in electric machinery control or application of control of electromagnetism a powerful person must face. The electronic apparatus that controls electric machinery and electromagnetism a powerful person needs to be close to the tall electric current that makes terminal application produces physics to move and voltage very much.
Harsh environment is the reality that a lot of electrical system in electric machinery control or application of control of electromagnetism a powerful person must face. The electronic apparatus that controls electric machinery and electromagnetism a powerful person needs to be close to the tall electric current that makes terminal application produces physics to move and voltage very much. Besides close quarters, these systems often can undertake maintaining (for example, the controller that service skilled worker changes dishwasher electromagnetism a powerful person board) , this left possibility for undesigned wiring mistake. Be close to tall electric current and voltage, increase the possibility with undeserved wiring, ask the design needs to had considered to press protection.
Build the system of efficient safety for compose, must use accurate electric current to detect amplifier comes monitoring the electric current in these application. Design of accurate amplifier circuit needs to had prevented to control an impact, but this kind of precision that protects circuit to may affect amplifier. Appropriately design, analysis and circuit of test and verify, can be being protected and the equilibrium is reached between precision. The article discusses circuit of two kinds of common protection, and how does the executive meeting of these circuit affect electric current to detect the precision of amplifier.
Electric current detects amplifier
Major electric current detects amplifier can handle Gao Gongmo tension (CMV) , but mishandle differs cent high to input voltage. In certain applying, the voltage of the input that need branch of existence spreader surpasses the case of the rated the biggest voltage of amplifier. This applies in industry and control of car electromagnetism a powerful person (in graph 1) very common, short circuit may cause trouble, detect electric current amplifier is exposed input voltage at needing branch high (its may reach as same as batteries potential) under. This differentia cent is pressed too may damage amplifier, below the circumstance that protecting circuit especially.
Graph 1. Control of electromagnetism a powerful person applies medium high-end electric current to detect
Press protective circuit too
Graph 2 indication electric current detect of amplifier press protection to join basically too. When v cent inputs voltage to appoint the biggest rating of amplifier more than, amplifier may be pulled interior to protect diode. If the input is brought,existence needs minute of voltage signal greatly between the foot, r1 of additional series connection resistor and R2 can prevent big electric current to flow into interior to protect diode.
Graph 2. Press protective circuit basically too
Protective circuit can the biggest rated voltage mixes susceptive to electric current of the biggest input follows parts of an apparatus and differ. General experience law is, had shed the electric current of diode of the in-house protection that need branch to answer with 3 MA in the limit of, unless norms book demonstrate is acceptability bigger electric current is worth. this value era enters the following equation, the value of computational R1 and R2:
Among them: VIN_MAX is to predict the biggest difference divides voltage. VRATED_MAX is the biggest rated voltage (0.7 V) . R is resistor of total series connection (R1 + R2) . For example, predict the biggest transient state inputs voltage to be 10 V suppose, criterion equality is:
If R = 3.1 KΩ , criterion according to equality 1, r1 and R2 = 1.55 KΩ . These numerical value of R1 and R2 are very great, considering the input impedance of specific amplifier, r1 and R2 will be right total system performance contributes bigger error.
A kind of method that reduces R1 and R2 is the foot is brought to increase the exterior protection diode with voltaic higher capability in the input, if pursue,3 are shown.
Graph 3. Buy inputs difference to divide those who protect diode to press protective circuit too outside
For example, use Digi-Key B0520LW-7-F Xiaoteji when diode (this diode can be handled be as high as 500 MA to voltaic) , is R value reduced to 20? .
The balance of systematic performance
In amplifier input end joins series connection resistor to may reduce certain performance data. In certain amplifier, r1 and R2 and in-house and accurate resistor establish ties. In other amplifier, maladjusted electric current and resistor produce maladjusted tension together. The parameter that suffers an effect more likely is gain error, in all the model is restrained than (CMRR) and maladjusted voltage.
To study the potential effect of series connection resistor, measured two electric current to detect amplifier, its input brings a foot to all be configured have protective resistance. If the graph is shown 4 times,the test that evaluates gain error, CMRR and maladjusted voltage is installed. This setting uses Agilent E3631A power source to provide 5 V only power source to parts of an apparatus, use source of Yokogawa GS200 accurate dc to produce poor cent to input voltage signal, use HAMEG HMP4030 to install CMV, use Agilent 3458A accurate avometer to measure electric current to detect the output voltage of amplifier.
Graph 4. Evaluate the test setting of gain error, CMRR and maladjusted voltage
So that measure resistor of additional series connection to be opposite,evaluate AD8210 and AD8418 the influence of error of gain of parts of an apparatus, CMRR and maladjusted voltage parameter.
Gain error
When inputting end to establish ties with amplifier when series connection resistor, the impedance of the input that need branch of they and amplifier forms voltage divider of a resistor together. This resistor voltage divider introduces an attenuation, its appear in circuit as additional gain error. The impedance of the input that need branch of amplifier is lower, this additional gain error is bigger.
The additional gain sum of errors that expresses 1 indication AD8210 to get via computation is actual gain error. Check AD8418 below belt and the case that do not take protective circuit respectively. Express the 2 additional gain sum of errors that show this amplifier gets via computation real gain error.
Actual measurement result is, deflection of AD8418 gain error 0.013% , and AD8210 deflection 0.497% . The input impedance of AD8418 and AD8210 is 150 KΩ and 2 KΩ respectively, accordingly, the error that AD8418 introduces will be far be less than AD8210.
In all the model is restrained than
Because electric current detects,amplifier often exposes the environment in tall CMV in, because this CMRR is one of the most important norms parameter. CMRR measures parts of an apparatus to check tall CMV and the capability that acquire best precision and property. Namely the two inputs end of amplifier brings to bear on when equal voltage, the output voltage that measures changes. CMRR definition is divided for difference gain and in all of modular gain than, express with DB normally.
Use the following equality to calculate the CMRR value of two amplifier:
Among them: ADM distributes gain for the difference of AD8210 and AD8418 (ADM = 20) . ACM is in all modular gain ΔVOUT/ΔVCM.
When inputting end to establish ties with amplifier when series connection resistor, of series connection resistor break those who deserve to be able to add internal resistance deserve to go up, this meeting affects CMRR.
Electric current detects the CMRR of amplifier AD8210 and AD8418 measures a result to if express,part 3 with the watch 4 are shown.
The result makes clear, the influence of resistor of additional and outer series is AD8418 CMRR is reduced, and relatively lesser to the influence of AD8210 CMRR. AD8418 turns into 89 DB, AD8210 keeps changeless almost (94 DB) . To securing gain parts of an apparatus, of AD8418 and AD8210 in all modular impedance is opposite taller, it is 750 KΩ and 5 MΩ respectively.
Express 1. AD8210 gain error
Express 2. AD8418 gain error
Express 3. AD8210 CMRR function (gain is 20)
Express 4. AD8418 CMRR function (gain is 20)
Express 5. The AD8210 that by the input maladjusted electric current and exterior impedance cause is additional and maladjusted voltage
Express 6. The AD8418 that by the input maladjusted electric current and exterior impedance cause is additional and maladjusted voltage
Maladjusted voltage
Should slant when buy electric current has shed exterior resistor, can produce the error tension that an inherent and as maladjusted as parts of an apparatus voltage establishs ties. For computation this one additional maladjusted voltage error, but will input maladjusted electric current (IOS, two inputs slant the difference of buy electric current) by the exterior impedance that brings a foot to go up with the input, if wait for type place to show below:
Among them: IOS is an input maladjusted electric current. R is additional and exterior impedance. Be based on AD8210 and AD8418 electric current to detect the maladjusted voltage that amplifier measures an outcome increases a quantity to if express,part 5 with the watch 6 are shown.
The result shows, the addition of AD8418 maladjusted voltage measures those who be more than AD8210 maladjusted voltage to increase an amount. By the input that AD8418 is 100 μA about maladjusted electric current causes this. Any additional impedance that input the series connection that cite a base are met as maladjusted as the input electric current is united in wedlock, produce error of additional and maladjusted voltage.
Conclusion
Bring in the input extra series connection resistance increasing on the foot is to protect electric current to detect amplifier is avoided had accepted the simple method that controls an impact. Can measure the effect that waits for function index to gain error, CMRR and maladjusted voltage, the extent of these influences and exterior resistor and use electricity detect amplifier type is direct and relevant. If the design is proper, circuit can improve poor cent of application to input voltage rating, and component amount increases very finite, very small also to the influence of precision.