Why Radial Selection Deserves Care

A radial leaded capacitor is the workhorse of a control board, supplying the bulk and the filtering for the low-voltage rails and the primary side of a supply. Because it is small, the choice is often made quickly, yet the voltage, the capacitance, the ESR and the lifetime all matter to the finished product. Choosing the wrong part raises the ripple, wastes board space and shortens the life. This guide walks through a repeatable method for selecting a CapXon radial leaded aluminum electrolytic capacitor.

Step 1: Fix the Voltage Class

Start with the rail voltage. The rated voltage must exceed the worst-case voltage with margin, so a 12 V rail uses a 16 V or 25 V part and a rectified high-voltage primary uses a 400 V or 450 V class. Higher voltage means a taller or wider can for the same capacitance, so the voltage choice and the mechanical fit are linked. Confirm the worst-case voltage against the real design, including the regulation tolerance and any transient.

Voltage Margin

Leaving too little margin shortens the life and risks a failure, while too much margin wastes capacitance and space, so a sensible margin is commonly twenty percent above the worst-case peak. A high-voltage primary often needs a slim can, which is why a slim high-voltage series such as the CapXon KY range exists.

Step 2: Choose the Capacitance and ESR

Size the capacitance from the ripple and the filtering you need for the load, then choose the ESR for the frequency of interest, because the ESR often dominates the impedance at the switching frequency. A low-ESR capacitor gives a lower ripple for the same capacitance and is the right choice at the output of a switching supply, while a general-purpose part is fine for a bulk rail. Balance the capacitance against the case size, because more capacitance means a bigger can.

Ripple Rating

The ripple current rating depends on the frequency and the case temperature, so use the datasheet multiplier and derate for the ambient. Keep the ripple within the rating, and verify the actual ripple on the bench because a low-ESR part carries more than a simple calculation suggests.

Step 3: Match the Case and Lead Spacing

Choose the case diameter and the lead spacing to fit the board: the standard 2.5 mm and 5 mm spacings cover most designs, and the case height must clear the enclosure. A radial capacitor mounts directly on the board with two leads, so the footprint is small, but the spacing must match the layout. Confirm the mechanical fit before you commit, because a wrong spacing forces a board change.

Series Choice

Choose the series by the life you need: the CapXon KM series is a general-purpose 105 °C range rated 2000 hours, the KY series is a slim high-voltage range for a height-limited primary, and the LE series is an ultra-long-life 105 °C range rated 12000 hours for equipment that must run for years, such as solar, industrial and lighting converters.

Step 4: Estimate the Lifetime

The life of an aluminum electrolytic capacitor depends on its core temperature, which is the ambient plus the ripple heating, so measure the case temperature at worst-case load and ambient and compare it with the derating curve. Because the life roughly doubles for every 10 °C reduction in core temperature, keeping the capacitor cool and the ripple low extends the life far beyond the datasheet endurance.

Getting Help

If you send your rail voltage, ripple, filtering and life target to our FAE team, we will propose a shortlist with capacitance, case size, lead spacing and lifetime and support the design-in. BeiLuo holds mainstream CapXon radial models in regional stock and ships them with an import declaration, a certificate of origin and a RoHS compliance file, and our engineers will review the choice with you before you commit to production.