Definition
A power-supply filter circuit in which a capacitor is the first component the rectified current encounters after the rectifier. The capacitor charges to the peak voltage of the pulsating DC and discharges through the load between peaks, smoothing the output into a steadier DC voltage. Capacitor-input filters produce a higher output voltage than choke-input filters but offer poorer voltage regulation under varying loads.
Plain English
A circuit that smooths bumpy DC power by placing a capacitor right after the rectifier. The capacitor stores charge during voltage peaks and releases it during the dips, giving a steadier output.
Context Anchor
Seen in aircraft electrical and electronics maintenance, especially in power-supply diagrams for radios, instruments, and other equipment.
Derivation
Called 'capacitor-input' because the capacitor is the first ('input') component the rectified current meets in the filter section. The name simply tells you the order: capacitor first, then any further filtering. This distinguishes it from a 'choke-input filter,' where an inductor (choke) is the first component instead.
Why Pilots Care
Provides stable power to radios and instruments, reducing noise and preventing equipment malfunction.
Analogy
Think of the capacitor as a small water tank fed by a sputtering pump. The pump pushes water in pulses, but the tank stays mostly full, so a steady stream comes out the other side.
Intuition Check
Do not read capacitor-input filter as a filter on the aircraft's main electrical input. It means the capacitor is the first smoothing part at the input side of the filter circuit, just after the current has been changed to direct current.
Example Sentence 1
The radio's power supply uses a capacitor-input filter to smooth the rectified DC before it reaches the internal circuits.
Example Sentence 2
During preflight checks the technician verified that the capacitor-input filter was functioning to keep radio interference low.