To verify that components are sufficiently protected against vibration damage, we must first set ourselves a standard of acceptability. This is a difficult task as vibration is often quite random in nature and varies with conditions and time. In some environments, such as in industry, vibration effects often originate from. The intensity of pure sinusoidal vibration can be expressed in three ways which are mathematically related; maximum amplitude or displacement,. Of all the common electronic components, capacitors are often the most susceptible to vibration damage, especially high-value electro-lytic types which can be tall and small-diameter for minimum footprint. Typical through-hole leaded types have relatively poor. Applications, where vibration resistance is critical, are becoming more common and manufacturer Panasonic is responding with vibration-proof components in their capacitor ranges.
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How do I choose a capacitor?
Depending on what you are trying to accomplish, the amount and type of capacitance can vary. The first objective in selecting input capacitors is to reduce the ripple voltage amplitude seen at the input of the module. This reduces the rms ripple current to a level which can be handled by bulk capacitors.
How to select a ceramic capacitor?
Taking the temperature and voltage effects is extremely important when selecting a ceramic capacitor. The Multilayer Ceramic Capacitor Selection section explains the process of determining the minimum capacitance of a capacitor based on its tolerance and dc bias characteristics.
How to select input capacitors?
The first objective in selecting input capacitors is to reduce the ripple voltage amplitude seen at the input of the module. This reduces the rms ripple current to a level which can be handled by bulk capacitors. Ceramic capacitors placed right at the input of the regulator reduce ripple voltage amplitude.
Only ceramics have the extremely low ESR that is needed to reduce the ripple voltage amplitude. These capacitors must be placed close to the regulator input pins to be effective. Even a few nanohenries of stray inductance in the capacitor current path raises the impedance at the switching frequency to levels that negate their effectiveness.
The capacitor physical size is directly proportional to the voltage rating in most cases. For instance, in the sample circuit above, the maximum level of the voltage across the capacitor is the peak level of the 120Vrms that is around 170V (1.41 X 120V). So, the capacitor voltage rating should be 226.67V (170/0.75).
As a general rule of thumb, keeping the peak to peak ripple amplitude below 75 mV keeps the rms currents in the bulk capacitors within acceptable limits. Load current, duty cycle, and switching frequency are several factors which determine the magnitude of the input ripple voltage.