Many people find it very confusing in the problem of analog signal separation. There may be many ways to isolate digital signals, but there are not many solutions for isolating analog signals, but they have to be isolated, generally based on the following requirements : 1. Isolation of interference sources; 2. Separate high voltage. There are many ways to isolate digital signals. The way to isolate analog signals is not as much as imagined. The key is that the cost of isolation is much higher than imagined. Especially in the case of accurate measurement, the isolation of analog signals is costly and unimaginable. I have been working on this kind of system for many years, and I have made a small summary of the isolation methods I know: Optocoupler 2. ADI's magnetic isolation chip, ADuMXXXX (XXXX is a digital code, such as I2C's ADuM1250); 3. Separate yourself with a transformer. The digital isolation method generally implements the isolation of the unidirectional digital signal. For the two-way digital signal, two isolation units are needed to realize the volume, which is very surprising; it is difficult to reduce the volume. Relative to the speed is very cost, if the speed is less than 100KHz, personally recommend the use of a common optocoupler such as Ps2501 to isolate the digital signal, good cost performance, isolation is also very high. Generally, the optocoupler isolation of the Ps2501 is above 3000V/RMS. However, if the frequency of the isolated digital signal is above 200KHz, it is not possible to use an optocoupler such as the Ps2501. To change the high-speed digital optocoupler, the price and cost are also up, which is not worthwhile. Therefore, the magnetic isolation chip of ADI can be used. The cheapest magnetic isolation chip costs $0.7 per channel, and the RMB is only 4 to 5 RMB. The high-speed optocouplers such as 6N137 and 6N136 are not cost-effective. A lot of PCB space is wasted for the isolation part. . The cost is around 4 or even higher, depending on your 6N137 purchase volume. However, the size of the magnetic isolation chip of the ADuM series is much smaller and the price is also superior. The only fly in the ointment is that the isolation voltage of the magnetic isolation chip can only reach about 1000V, which is a headache. If it is only to isolate the interference source, it is naturally no problem. If it is to isolate high voltage, then carefully consider the design. The method of isolation by an isolation transformer is not used by ordinary people because there is no economic benefit at all. It has only one advantage, that is, the isolation voltage can be made very high. Generally, only the inverters, inverters and other IGBTs are driven. It is necessary to isolate a very large voltage, which exceeds 5000V. Because the general chip and optocoupler can not be realized. 1. Linear optocoupler; 2. Isolation amplifier; 3. Frequency conversion and voltage conversion + digital isolation; 4. Flying capacitors; 5. Adopt DA/AD+ digital isolation method to realize the sampling and recovery of analog signals, and then realize the isolation method; 6. Linear isolation achieved by ordinary optocouplers. Linear optocouplers, friends who have done isolation know. As the previous TIL300, it seems that it has not been produced yet. You can choose Vishay's IL300 as an alternative. As a linear isolation of general analog signals, it is a good choice. In general, linear optocouplers require two op amps and some precision resistors to form the appropriate circuit to complete the signal isolation. It is also only one-way isolation. The price of IL300 is about ten yuan. If you want better temperature characteristics, you need two better op amps, so the cost of the whole isolation is 30RMB/Ch per channel, and the isolation frequency is about 200kHz. The linearity is not ideal, and the accuracy of 0.1% is difficult to guarantee; but the manual says that it can reach 0.01% servo precision. In fact, because of the temperature effect, the linearity is +/- 0.5%, so children with higher isolation linearity can't choose this method. But it is ok for most occasions; Isolation amplifier, this is the ultimate baby, there are many manufacturers, a small Chinese factory to produce such a thing. Linearity can reach 0.1%, compared to the isolation amplifiers of TI and ADI, the cost of these things is very high. TI has one of the lowest price isolation amplifiers in the world, ISO124. Isolation amplifiers, stable performance, good linearity, most can reach or far exceed 0.1%, can reach 0.01%; but the price is at least 40RMB / Ch, ADI is even more outrageous, probably to 40dollar /Ch, for manufacturers of general industrial products, it is really prohibitive. The third method is similar to the fifth method in that it converts the analog signal into a digital signal and then isolates the digital signal. The digital signal is restored to an analog signal, so this also means that the circuit is very complicated. But from the perspective of isolation, it should be a more reasonable way of isolation. At least in terms of cost and accuracy, it has the best combination with isolation amplifiers. Both the frequency-frequency conversion and the frequency-to-voltage conversion are very expensive. Therefore, this device is not suitable for low-bandwidth signal conversion; the voltage-frequency and frequency-voltage conversion do not require the participation of the single-chip microcomputer, and the circuit is simpler and more reliable. If AD/DA conversion is used for recovery, the participation of control circuits such as a microcontroller or an FPGA is required. From the perspective of development, more energy is required. Compared with the method of frequency-to-voltage conversion, the comparison of the signal bandwidth is related to the bandwidth of AD/DA. But choose the right chip and microcontroller, such as the 32-bit single chip of cortex-M0, about 40MHz, a few dollars. With the appropriate AD/DA, the cost can be controlled at 30RMB/ch, but the effect is much better than IL300, mainly because the isolation linearity can have a very good guarantee. Flying capacitors, flying capacitors have not been tried, but flying capacitors are also a special isolation scheme. Compared to other isolation schemes, the first is that there is no need to isolate the power supply; the second is that the circuit is simple. The flying capacitor uses the analog signal as a source to charge a suitable capacitor. After charging, the flying capacitor is switched to the side of the measuring circuit and completely disconnected from the circuit for charging the flying capacitor. The capacitor discharges the measuring circuit. The measuring circuit measures the voltage of the capacitor. That is, the isolation of the voltage signal is achieved. The core of this circuit is to switch capacitors and control the switching time. It is best to use relays, but ordinary relays have a limited life, and this kind of play is definitely scrapped. To use a wet reed relay; the wet reed relay should not be a cheap thing, I have not tried this method, but in theory it is completely feasible. But the signal bandwidth is small. Maybe only 10Hz. Ordinary optocoupler only uses a special idea, using another optocoupler to do the feedback and compensation of the first optocoupler. This method, personally feel that the isolation of the general signal is OK, because there is no guarantee such as Datasheet, in fact, large Batch application is difficult to guarantee consistency and stability. It is only used when the linearity requirements are very low. The cost should be the lowest in all analog signal isolation schemes, and can be less than 5 bucks/ch. LED Tunnel light,Tunnel light of high protection grade Kindwin Technology (H.K.) Limited , https://www.ktlleds.com