When I was looking for a job in the year I graduated, I participated in an interview with a foreign company, and I had a good conversation at the beginning. Suddenly an interviewer asked me what the resistance values are. At that time, I was confused, wondering if the resistance value is not Arbitrary? Then I was rejected.
After I worked, I learned that the original resistance has the resistance standard, the capacitor has the capacitance standard, and even the wire has the wire standard. All in all, there are standards for any product!
The standard of resistance was originally formulated by the EIA of the United States. The standard mainly includes the following specifications. One is the error range. The previous process is poor, and the product made may have a 20% error. For example, if you choose a 100 ohm resistor , The measured value is between 80~120. Later, with the improvement of technology, 5% accuracy and 1% accuracy are widely used, and of course there are 0.5% and 0.1% accuracy. The higher the accuracy, the more expensive.
The second standard is how the resistance value is formulated. Depending on the accuracy, the number of options available between 1 and 10 is different. The number of options for low accuracy is less, which is easy to understand. For example, if you choose a 100 ohm resistor If the accuracy is 5%, it may be 105 ohms at most, so there is no need for another 102 ohm resistor. According to the different resistances of the optional number, it is mainly divided into the following series
| E SERIES | TOLERANCE | NUMBER OF VALUES IN EACH DECADE |
|---|---|---|
| E6 | 20% | 6 |
| E12 | 10% | 12 |
| E24 | 5% | 24 |
| E96 | 1% | 96 |
| E192 | 0.5% and higher | 192 |
The benchmark values under different standards are as follows
| E6 | ||
|---|---|---|
| 1.0 | 1.5 | 2.2 |
| 3.3 | 4.7 | 6.8 |
========================================
| E12 | ||
|---|---|---|
| 1.0 | 1.2 | 1.5 |
| 1.8 | 2.2 | 2.7 |
| 3.3 | 3.9 | 4.7 |
| 5.6 | 6.8 | 8.2 |
========================================
| E24 | ||
|---|---|---|
| 1.0 | 1.1 | 1.2 |
| 1.3 | 1.5 | 1.6 |
| 1.8 | 2.0 | 2.2 |
| 2.4 | 2.7 | 3.0 |
| 3.3 | 3.6 | 3.9 |
| 4.3 | 4.7 | 5.1 |
| 5.6 | 6.2 | 6.8 |
| 7.5 | 8.2 | 9.1 |
========================================
| E96 | ||
|---|---|---|
| 1.00 | 1.02 | 1.05 |
| 1.07 | 1.10 | 1.13 |
| 1.15 | 1.18 | 1.21 |
| 1.24 | 1.27 | 1.30 |
| 1.33 | 1.37 | 1.40 |
| 1.43 | 1.47 | 1.50 |
| 1.54 | 1,58 | 1.62 |
| 1.65 | 1.69 | 1.74 |
| 1.78 | 1.82 | 1.87 |
| 1.91 | 1.96 | 2.00 |
| 2.05 | 2.10 | 2.16 |
| 2.21 | 2.26 | 2.32 |
| 2.37 | 2.43 | 2.49 |
| 2.55 | 2.61 | 2.67 |
| 2.74 | 2.80 | 2.87 |
| 2.94 | 3.01 | 3.09 |
| 3.16 | 3.24 | 3.32 |
| 3.40 | 3.48 | 3.57 |
| 3.65 | 3.74 | 3.83 |
| 3.92 | 4.02 | 4.12 |
| 4.22 | 4.32 | 4.42 |
| 4.53 | 4.64 | 4.75 |
| 4.87 | 4.99 | 5.11 |
| 5.23 | 5.36 | 5.49 |
| 5.62 | 5.76 | 5.90 |
| 6.04 | 6.19 | 6.34 |
| 6.49 | 6.65 | 6,81 |
| 6.98 | 7.15 | 7.32 |
| 7.50 | 7.68 | 7.87 |
| 8.06 | 8.25 | 8.45 |
| 8.66 | 8.87 | 9.09 |
| 9.31 | 9.53 | 9.76 |
更多的电阻值，在这些基础电阻值上乘以10的x次方。
比如8.06x1000=8.06K，8.06x100=806欧姆，8.06x10=80.6欧姆，等等。
在电路系统中的电源部分，经常会用到两个电阻分压实现负反馈电路的情况，恰到好处的选取两个电阻阻值有时并不是一件容易的事，
常见的LDO手册中，调整输出电压的方法如下图所示
好在下面这个网址提供一个计算分压电阻的小工具。
只需要填写输入电压、输出电压然后就会自动匹配出相应的电阻阻值。
http://www.ti.com/download/kbase/volt/volt_div3.htm