Basic knowledge of EMI power filter
Rated voltage
Rated voltage refers to the highest voltage value that can be continuously applied to a filter within the specified frequency and operating temperature range.
Rated current
Rated current refers to the safe allowable current that a filter can pass through at a specified frequency and voltage, with an ambient temperature of 40 ℃.
Test voltage
The test voltage, also known as the usual withstand voltage test, is used to verify the insulation characteristics of the filter and the high voltage resistance of its internal components. During testing, the voltage starts from zero and rises to the specified test voltage value at a rate not exceeding 150V/S to start timing. There are usually two specifications, one is a typical test with a time of 60 seconds. Another type is product testing, which takes 3 seconds. For detailed information, please refer to relevant IEC documents.
insulation resistance
Insulation resistance refers to the resistance between the phase and neutral lines of a filter and the ground. Usually tested with a dedicated insulation resistance meter.
Maximum leakage current
Leakage current refers to the maximum current (usually measured at 250VAC/50Hz) that passes through the filter phase and neutral lines to ground (casing) at a given voltage and frequency. To ensure safety, there are different regulations for this indicator for filters of different types and applications. General users do not have a device for measuring single channel leakage current, and the test value is the value of the overall filter, which should be corrected.
temperature rise
The general indicator is: Δ t<30 ℃.
insertion loss
Insertion loss is an indicator of the filtering effect of a filter, usually expressed in decibels or frequency characteristic curves. It refers to the power ratio or port voltage ratio of the power supply to the load before and after the filter is connected to the circuit. IL=10IgPo/P2 (dB) or IL=20IgVo/V2 (dB), sPo, P2, Vo, V2 respectively represent the power and voltage at the load end before and after the filter is connected. Laboratory measurements are generally conducted in a 50/50 Ω system.
Interference form
To understand the related issues of conducted interference, it is necessary to understand the two modes of conducted signals: co model and differential model. Differential mode interference (also known as symmetrical interference) refers to interference signals in the system phase lines, where differential mode currents enter from one phase line and exit from another, independent of the ground wire. Common mode interference (also known as asymmetric interference) generates a voltage between each phase line, neutral line, and ground, causing common mode current to flow from the interference source to the ground line and back to the phase line from the ground line.
Climate category
According to DINIEC68 Part 1, the climate category consists of three numbers, such as 25/85/21, where 25 represents the lower limit of the operating temperature of -25 ℃. 85 represents the upper limit of working temperature+85 ℃. 21 indicates that it can last for more than 21 days at a relative humidity of 90-95%. Traditionally, the impedance relationship is described under a device with a termination impedance of 50 Ω at both ends of the filter, as this is convenient for testing and complies with RF standards. But in practical applications, ZS and ZL are very complex and may be unknown at the frequency points to be suppressed. If one or both ends of the filter are connected to reactive elements, resonance may occur, causing insertion loss at certain frequency points to become insertion gain. If the high-frequency characteristics of the components that make up the source or load may be clearly defined, the differential mode impedance can be predicted, but the common mode impedance composed of parasitic reactance of cables or structural components is basically unpredictable.
