1. Analysis of the filtering ripple capacity of solid aluminum capacitors

For switching power supplies, miniaturization of circuits is the future direction, and the number and size of capacitors used in circuits should be minimized.

The following is a comparison of the filter's filtering ripple capability at different ambient temperatures in high-frequency circuits. The circuit used in the experiment is shown in Figure 1. Using a general step-down switching power supply, the output smoothing capacitor C uses PolyCap solid aluminum capacitors, Low ESR liquid aluminum capacitors, and Low ESR tantalum capacitors at ambient temperatures of 25 ° C and -25 ° C, respectively. The output ripple voltage of the case is used to evaluate the filter ripple capability of these three capacitors.

　　Figure 1 Experimental circuit diagram

(1) Experimental methods:

(1) The capacitor under test in Figure 1 uses a PolyCap solid-state aluminum capacitor 6.3V220μF (Φ6.3mm × 7mm) to test the ripple voltage at each ambient temperature;

(2) At the corresponding ambient temperature, the Low ESR liquid aluminum capacitor and the Low ESR tantalum capacitor are selected so that the output ripple voltage reaches the above test value when using the solid capacitor.

(2) Experimental results:

Table 1 Comparison of the filtering ability of each capacitor at ambient temperature of 25 ° C, -25 ° C and 75 ° C

It can be seen from the above experimental results that the filtering power of 1pcs solid aluminum capacitor is equivalent to 2pcs tantalum capacitor and 2~7pcs large capacity liquid aluminum capacitor, which indicates that the solid aluminum capacitor can significantly reduce the circuit and ensure that the circuit is different. Stable operation at temperature.

2. Application of solid aluminum capacitors in low-pass filter circuits

The power supply in the digital circuit is prone to noise, so low-pass filtering is required in the digital circuit to prevent high-frequency noise from entering the analog circuit. Low-pass filtering has LC filtering and RC filtering, which are compared below.

　　Figure 2 LC filter                                                             Figure 3 RC filter

　　The ESR of the capacitor in the low-pass filter circuit greatly affects the attenuation effect. The lower the ESR of the capacitor, the closer to the ideal attenuation rate. Since the ESR of solid aluminum capacitors is very small, the application of solid aluminum capacitors in low-pass filter circuits has obvious advantages.

Figure 4 Actual attenuation rate

The low-pass filtering effect is compared with two capacitors of the same specification: (a) PolyCap solid aluminum capacitor 16V100μF, ESR measured value 12mΩ; (b) liquid aluminum capacitor 16V100μF, ESR measured value 689mΩ. The result is shown in Figure 5:

(1) LC filtering (L=10uH)

　　PolyCap solid aluminum capacitor                                          Liquid aluminum capacitor

　　(2) RC filtering (R = 5.6 Ω)

　　PolyCap solid aluminum capacitor                                                Liquid aluminum capacitor

Figure 5 Comparison of low-pass filtering effects of two capacitors

As can be seen from the above figure, in the high frequency region, the solid aluminum capacitor has much better attenuation than the liquid aluminum capacitor.