Selection of capacitor for power supply(II)

To select the appropriate capacitance value, the rated DC voltage, the allowed voltage ripple and the charge / discharge cycle should be checked. However, the following parameters should be considered when choosing an electrolytic capacitor for this application.

The ripple current of the capacitor in typical power supply is a combination of ripple current on various frequencies. The RMS value of the ripple current determines the temperature rise of the capacitor.

One common mistake is to calculate the RMS current load by adding the squared value of the ripple current on each frequency. In fact, it must be considered that the ESR of the capacitor will decrease as the ripple frequency increases.

The correct way is to estimate the ripple current at high frequency (up to 100HZ) according to the frequency chart of ripple factor. The estimated current square value is used to determine ripple current. This is the real current load.

The relationship between the ripple current load, the ambient temperature and the probability life is precisely defined. Under the actual working conditions, the probability life is determined by the ripple current load and the ambient temperature, and the published probability life is taken as the absolute value.