原创 电阻电容标准值

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来自TI公司：如何选择滤波器的R和C

How do I select R's and C's for a Filter Circuit?

Problem:
How do I select R's and C's for a Filter Circuit?

Solution:
Texas Instruments Applications has a spreadsheet to perform this calculation for the designer. To use the spreadsheet, simply click on the link above. Users that have Microsoft Excel 2000 installed on their system should have the spreadsheet open automatically. Other users can save the file by right clicking the mouse and saving the target. Once the window is open:

• Enter the corner or center frequency into the cell to the right of the word "Frequency".
  
  
• The designer will be presented with one or more mantissa values in four different categories on the right:
  
  
  • 5% Capacitors and 1% Resistors (E96)
  • 5% Capacitors and 5% Resistors (E24)
  • 10% Capacitors and 10% Resistors (E12)
  • 20% Capacitors and 20% Resistors (E6)
  
  It is up to the designer to know the accuracy required by the filter. Some applications, like high Q notch filters may require 1% resistors AND 1% capacitors (which usually are sold on 5% increments). Audio circuits may do fine with 10% components. If more than one combination is presented, it is because they produce identically low errors.
  
  
• The designer will also be presented with a range of values for the resistor exponent (below the frequency blank). The capacitor exponent values are fixed. Filters are scalable - that is the resistors can be reduced an order of magnitude if the capacitors are increased by a decade. There are several combinations of exponents. Some may be nonsense, but others represent a trade-off between power consumption and noise. It is up to the designer to decide. There is general guidance to the right of the exponents.
  
  
• The designer should select a mantissa for the resistor, and one for the capacitor, and enter them in the selected resistor and capacitor manissa blanks.
  
  
• The designer should select an exponent for the resistor, and one for the capacaitor, and enter them in the selected resistor and capacitor exponent blanks.
  
  
• The designer will then be presented with an actual frequency and error for the resistor and capacitor values they have selected. If all is well, the error should be small. If not, the designer needs to check what the entered in the "selected resistor and capacitor" blanks and re-enter appropriate values.

For designers using older versions of Excel, an Excel 95 version is available. This spreadsheet is offered on an "as-is" basis. Extensive testing has proved that it produces good values for RC, but not necessarily the best, or all of the combinations that are best. No warranty of any sort is expressed or implied. The designer uses it at their own risk.

Hopefully, the designer now has the answer to the question: What type of filter do I need?