Electrolytic Capacitors

Electrolytic Capacitors Points : Electrolytic Capacitors In an electrolytic capacitor two sheets of aluminum foil, separated by fine gauze soaked in an electrolyte (ammonia solution or boric acid solution), are rolled up and encased in an aluminum or ceramic or plastic tube. When assembled a direct voltage is applied to the capacitor terminals, and this causes a thin layer of aluminum oxide to be formed on the surface of the positive plate next to the electrolyte. The aluminium oxide is the dielectric. The electrolyte and the positive foil are the capacitor plates. The extremely thin oxide layer of dielectric (approx 0.00001 cm thick) gives a large value of capacitance for small physical dimensions of the capacitor. They can be used only for d.c. They should be connected with correct polarity. (The positive terminal is usually marked red on the capacitor). If incorrectly connected, gas forms with in the electrolyte and the capacitor may burst. They have the advantage of small size and low cost. However, their working voltage is low and leakage current high. The range of capacitance is from around 1 uF to 2000 uF and working voltage up to 400 volt d.c. Their main field of application is in electronic circuits and filter circuits.