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当我们做一个分压器测量电压超过3.3或5V时，我们使用分频器并将电压馈送到运算放大器缓冲器或直接送到PIC ADC。这是选择电阻器值的标准，例如，如果我们需要50伏的5V，我们可以选择9K和1K或18K和2K安。其他组合值。是否存在任何基于电压源和目的地的敲击或任何其他方法的规则。谢谢。
以上来自于百度翻译 以下为原文 When we are making a voltage divider for measuring voltages beyond 3.3 or 5Volts, we use divider and fed the voltage to op-amp buffer or directly to PIC ADC. which is the criteria for choosing the resistor values, for example if we need 5V from 50 volts we can choose 9k and 1K or 18K and 2K an many other combination values. is there exists any rule of thump or any other methods based on source and destination of the voltages. Thanks. 
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9个回答
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大多数PIC ADC指定最大源阻抗约为5K-10K，这将是ADC输入到地的电阻器。如果在输入端增加一个电容器，可以提供一个稍高的源阻抗，以提供对采样电容器充电所需的电流。这对于缓慢变化的直流信号很有效。为了在高采样率和短采集时间下精确测量AC信号，必须仔细选择电容器，以提供足够的带宽，并仍然过滤高频噪声。
以上来自于百度翻译 以下为原文 Most PIC ADCs specify maximum source impedance of about 5k-10k. That would be the resistor from the ADC input to ground. You can use a somewhat higher source impedance if you add a capacitor to the input, to provide the current needed to charge the sampling capacitor. That works well for slowly varying DC signals. For accurate measurement of AC signals at high sampling rates and short acquisition times, the capacitor must be carefully chosen to provide adequate bandwidth and still filter high frequency noise. |
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它是除法器的戴维南等值。你还需要考虑对被测电路的影响。你不想通过测量电路排水一个电池。同样，保持电流流过ADC尽可能低，因为流过分配器的电流的一小部分，肯定小于10%。否则，你会偏爱阅读，浪费你在低容忍电阻上的钱。
以上来自于百度翻译 以下为原文 It's the Thevenin equivalent of the voltage divider. You also need to consider the effect on the circuit being measured. You don't want to drain a battery through the measurement circuit. Also, keep the current flowing into the ADC as low as possible as a fraction of the current flowing through the divider, certainly less than 10%. Otherwise you will bias the readings and waste any money you spent on low tolerance resistors. |
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2018-9-6 16:48:57
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ADC输入到地面的电阻将是ADC的输入阻抗，源阻抗将是被测电压与ADC的输入之间的电阻，也就是对采样Cap充电的阻抗。
以上来自于百度翻译 以下为原文 The resistance from the ADC input to ground would be the Input Impedance of the ADC. The source Impedance would be the resistance between the voltage being measured and the input to the ADC. That is the impedance that charges the sampling Cap. |
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较小的电阻器将消耗更多的功率。较大的电阻器将为ADC或运算放大器提供更高的输入阻抗。它们也会产生更多的噪音（但实际上这是很小的量）。根据对你来说重要的是，你的电阻会变大或变小。
以上来自于百度翻译 以下为原文 Smaller resistors will consume more power. Bigger resistors will provide higher input impedance for the ADC or for Op Amp. They will also produce more noise (but this is actually very small amount). Based of what's important to you, you make your resistors bigger or smaller. |
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我认为参考是分压器的小腿，在被测量的电压（形成分压器的两个电阻的结）和ADC的输入之间没有电阻。再次，源阻抗是分压器的戴维南等值。
以上来自于百度翻译 以下为原文 I think the reference was to the lower leg of the voltage divider. There is no resistance between the voltage being measured (the junction of the two resistors forming the voltage divider) and the input to the ADC. Again, the source impedance is the Thevenin equivalent of the voltage divider. |
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+ 1…这是上电阻和下电阻的并联电阻。
以上来自于百度翻译 以下为原文 +1 ... which is the parallel resistance of the upper resistor and the lower resistor. |
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嗨+ 1…它是上电阻和下电阻的并联电阻。+1，如果你的分频器从你的PIC工作的同一电源上采样电压，它是非常直的。当你仅用接地重新采样一个“外部”电压时，会变得更复杂一些。正如OP所提到的，作为一个例子，一些50V，它的尾随情况，和“并行”得到的计算要复杂得多。至少是“上”阻抗。
以上来自于百度翻译 以下为原文 Hi +1 ... which is the parallel resistance of the upper resistor and the lower resistor. +1. Its quite straight forward if your divider is sampling voltage from the same power supply from wich your PIC is working. Gets a bit more complicated when you are sampling an "outside" voltage with only the ground referenced. As the OP mentioned, as an example, some 50V, its certailnly the case, and the "parallel" gets a bit more complex to calculate. At least the "upper" impedance. |
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最佳解决方案：使用高（ER）值电阻器（着眼于它们的噪声贡献），然后用所提到的OPAMP电压跟随器对它们进行缓冲以驱动ADC输入。这将最大限度地减少分压器的电流消耗，并确保ADC前端具有良好的低阻抗源。
以上来自于百度翻译 以下为原文 Best solution: Use high(er) value resistors (with an eye toward their noise contribution) and then buffer them with the opamp voltage follower you mentioned to drive the ADC input. This will minimize the current consumption of the voltage divider and insure the ADC front end has a nice low impedance source. |
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