Common problems in the selection of film capacitors

Common problems in the selection of film capacitors

A. improper selection of rated voltage

The rated voltage is improperly selected, and the most frequent place is the resonant circuit part (C5). R&D personnel should base on the equipment’s rated power, input voltage, circuit topology, inverter control method, load material, load magnetic load rate, circuit Q value and other parameters As a preliminary calculation after comprehensive consideration. After the prototype meets the requirements initially, you need to use an oscilloscope to add a high-voltage voltage probe to actually measure the peak-to-peak voltage, peak voltage, and root mean square voltage across the resonant capacitor when the device is at maximum power. Parameters such as resonant frequency are used to determine whether the selected resonant capacitor model and parameters are correct.

B. Improper selection of rated current

The rated current is improperly selected, and the most common places are C3 (DC support) and C5 (resonance). If the actual required current value is greater than the allowable current value of the capacitor, it will cause serious heating of the capacitor and long-term high temperature operation, resulting in The life of the capacitor is greatly reduced, and it will blow up or even catch fire. In the equipment research and development, you can use a dedicated current probe or other methods to measure the actual peak current and the root mean square value of the current, and then adjust the parameters of the capacitor. Finally, the temperature rise of the capacitor can be measured in the full power aging test of the equipment, and the selection of the capacitor can be determined according to the allowable parameters of the temperature rise of the capacitor. (Comprehensive evaluation of current measurement and temperature rise)

C. improper wiring

The improper wiring method mainly occurs in the use of multiple capacitors in parallel. Due to the wiring method and the inconsistent wiring distance and other factors, each parallel capacitor is inconsistent in the circuit. It is finally reflected in the multiple parallel capacitors, and the temperature of each capacitor is inconsistent. The rises are inconsistent. The temperature of the capacitors in individual locations is too high and burned. Therefore, it is necessary to connect and connect the capacitors in parallel, and try to achieve current sharing and improve the service life of the capacitors.Common problems in the selection of film capacitors