A Practical Linear Isolation Detection Circuit

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A Practical Linear Isolation Detection Circuit [Copy link]

Abstract: A circuit with isolation function and can be used to detect feedback DC voltage and current signals is proposed. This circuit can replace the precision linear optocoupler TIL300. Experiments are carried out on this basis, and the experimental results prove that this circuit has the advantages of simple structure, high precision, good linearity and low price.

Keywords: Isolation amplifier Optocoupler

With the development of power supply technology, power supply equipment such as switching power supplies and UPS are increasingly widely used in power systems and communication systems. These devices must detect the voltage and current signals of the main circuit without exception. The detection circuit is the interface between the main circuit and the control circuit, and is an indispensable and important component of the power supply equipment. The detection circuit must meet the following requirements:

(1) It must have high accuracy and linearity. In order to achieve high voltage and current stabilization accuracy and have good dynamic response characteristics, most modern power supplies introduce voltage and current to participate in the feedback control of the system. The accuracy and linearity of the detection circuit determine the output accuracy and stability of the entire power supply to a certain extent.

(2) It must have an isolation function. The main circuit and control circuit of most power supplies are electrically insulated from each other. Otherwise, the power supply will not work properly due to the interference of the main circuit on the control circuit, and may even endanger the personal safety of the commissioning personnel.

At present, there are many isolated sensors available on the market, such as isolation amplifiers (TPS5904, AD202), voltage Hall, current Hall, etc. Among the above devices, AD202 and Hall elements have the advantages of good performance, high reliability, accurate measurement, and wide application range. But its high price makes most users stay away. Although TPS5904 is relatively cheap, its linearity is relatively poor. Only TI's TIL300 precision linear optocoupler can accurately detect DC signals, has good isolation effect, and is cheap. Therefore, many designers prefer TIL300 as a detection element for detecting and feedback DC voltage and current when selecting devices.

However, with the discontinuation of the TIL300 production line, users who used TIL300 before have to choose other devices, and there are no other components in the current electronic component market that can match the price and performance of TIL300, which brings great inconvenience to users. Based on this situation, this paper proposes a detection circuit that can replace TIL300. This circuit uses ordinary optocouplers and applies feedback control principles. It has the characteristics of low price and good linearity, and can replace the original TIL300 to a certain extent.