<Tr> <Td> </Td> <Td> This article needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (October 2014) (Learn how and when to remove this template message) </Td> </Tr> <P> A flyback diode (sometimes called a kickback diode, snubber diode, commutating diode, freewheeling diode, suppressor diode, suppression diode, clamp diode, or catch diode) is a diode connected across an inductor used to eliminate flyback, which is the sudden voltage spike seen across an inductive load when its supply current is suddenly reduced or interrupted . It is used in circuits in which inductive loads are controlled by switches, and in switching power supplies and inverters . </P> <P> Fig. 1 (above left) shows an inductor connected to a battery, a constant voltage source . The resistor represents the small residual resistance of the inductor's wire windings . When the switch is closed, the voltage from the battery is applied to the inductor, causing current from the battery's positive terminal to flow down through the inductor and resistor . The increase in current causes a back EMF (voltage) across the inductor due to Faraday's law of induction which opposes the change in current . Since the voltage across the inductor is limited to the battery's voltage of 24 volts, the rate of increase of the current is limited to an initial value of d I d t = V B L (\ displaystyle (dI \ over dt) = (V_ (B) \ over L)) So the current through the inductor increases slowly as energy from the battery is stored in the inductor's magnetic field . As the current rises more voltage is dropped across the resistor and less across the inductor, until the current reaches a steady value of I = V B / R (\ displaystyle I = V_ (B) / R) with all the battery voltage across the resistance and none across the inductance . </P> <P> When the switch is opened (fig. 2 above right) the current drops rapidly . The inductor resists the drop in current by developing a very large induced voltage of opposite polarity to the battery, positive at the lower end of the inductor and negative at the upper end . This voltage pulse, sometimes called the inductive "kick", which can be much larger than the battery voltage, appears across the switch contacts . It causes electrons to jump the air gap between the contacts, causing a momentary electric arc to develop across the contacts as the switch is opened . The arc continues until the energy stored in the inductor's magnetic field is dissipated as heat in the arc . The arc can damage the switch contacts, causing pitting and burning, eventually destroying them . If a transistor is used to switch the current, for example in switching power supplies, the high reverse voltage can destroy the transistor . </P>

What is the purpose of diode in relay