In recent years, digital isolation chips have been trusted by engineers in the fields of industry, medical care, and automobiles. Digital isolation chips are gradually replacing traditional optocouplers because of their small size, high integration, low power consumption, and high communication speed. The digital isolation chip is the core device involved in high voltage security in the system, so it needs to be strictly screened when it leaves the factory. The UL1577 safety standard clearly stipulates that when the product leaves the factory, it must be tested under the insulation withstand voltage for 60s or 1.2 times under the insulation withstand voltage. The product that passes the high voltage test can be shipped.
Take the product with isolation strength of 3000Vrms as an example. It needs to be subjected to high voltage test under 3000Vrms, frequency of 60Hz AC voltage for 60s or 3600Vrms and frequency of 60Hz AC voltage for 1s. . The high voltage test specified by UL1577 is to detect the leakage current of the insulating layer. If the insulation voltage of the digital isolation chip can withstand the test high voltage, the leakage current of the detected insulation layer will be relatively small. This value is usually uA level, because the low frequency AC high voltage is applied, as long as the isolation sides exist. With a certain parasitic capacitance, there will be AC ​​leakage current. However, if the insulation voltage of the digital isolation chip cannot withstand the corresponding high voltage, the insulation layer will have an uncontrollable leakage current due to the high voltage, and finally the isolation tape will be damaged. Generally, the insulating layer of the digital isolation chip has high environmental cleanliness requirements during production, and there is no possibility of bubbles or voids, so as to ensure good insulation effect and long insulation life.
However, in the actual production process, it is difficult to ensure that all the chips 100% guarantee that the insulating layer has no bubbles or voids, and the existence of these voids or bubbles may cause the insulation performance to decrease, but these voids or bubbles cannot pass the method of detecting the high-voltage leakage current. Detected. When high voltage is applied to both ends of the insulating medium, partial discharge (Partial Discharge) occurs due to the presence of these bubbles or voids. The slight partial discharge has less influence on the insulation of the power equipment, and the insulation strength decreases slowly; Discharge will cause the insulation strength to drop quickly. This is an important factor in the insulation damage of high voltage power equipment.
Partial discharge is accompanied by the generation of electrical impulses, ultrasonic waves, electromagnetic radiation, light, chemical reactions, and local heating, which is a sign of aging of electrical components. The applied voltage of the partial discharge detection is not the insulation withstand voltage value, but the working voltage applied to the insulating layer, because only the working voltage is long-term acting on the insulating layer, and may cause repeated charging and discharging of the defective product, eventually resulting in The insulation fails prematurely. Therefore, VDE0884-10 safety regulations require partial discharge detection in addition to high-voltage leakage current testing during product factory testing. The test voltage for partial discharge detection is 1.875 times the peak operating voltage, the test time is 1 s, and the target value of the detection result is the magnitude of the leakage charge.
Figure 1. Partial discharge test circuit
All products of the digital isolation chip NSi81xx series of Suzhou Nanochip Microelectronics Co., Ltd. are strictly tested in accordance with safety regulations. In order to further improve the reliability of the product, the FT test of the NSi81xx series of digital isolation chips has been added to the high-voltage insulation test based on the conventional low-voltage performance test, including the insulation withstand voltage test and the partial discharge test. The high reliability of digital isolation chips provides a solid guarantee. In order to ensure the reliability of the digital isolation chip from the factory, Nanochip Microelectronics has established an effective and reliable high voltage test system, especially the partial discharge test system. This system not only needs special detection instruments, but also requires automatic test handlers. Special transformation, the high-voltage test system of the digital isolation chip has been approved by domestic and foreign safety agencies.
Figure 2. Digital isolation chip factory FT high voltage insulation test waveform
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