Capacitance (Timing Circuits) Essay Example | Topics and Well Written Essays - 500 words

Capacitance (Timing Circuits) - Essay Example For capacitance derived unit is useful for expressing the charge (unit of charge is Coulombs)that can be transferred to an object per unit of voltage ( unit of voltage is in Volts) and thus a unit which we got from this ratio is known as Farad. Each capacitor having two parallel plates and will have capacitance equal to  8.85 Ï F/m, times the area of one of the plates, divided by the distance between them. When sharing the charge applied to one capacitor with a second capacitor, charge is conserved, therefore Vf * (C1 + C2) = Vi * C1. When discharging a capacitor through a resistor, V(t) = V0 * e-t/RC. When charging a capacitor through a resistor, V(t) = Vf – Vf * e-t/RC (â€Å"Courseworkbank†). In timing circuits there are two possibilities either we are controlling the rate of response of the capacitor or controlling the rate of voltage across the capacitor. If a series combination of a resistor and capacitor are present such type of circuit is simplest timing circuit. The amount of time to charge the capacitor to 63% of the input voltage as well as it is equal to the resistance times the capacitance is known as time constant T=RC.Varying the values of resistance and capacitance ultimately results in time ranging from microseconds to weeks. The important characteristics of capacitor are: This timer circuit is similar to the 5 to 30 minute timer except that when switch S1 is closed, the on/off action of the circuit will continue indefinitely until S1 is opened again. A 7555 time and low leakage type capacitor for C1 must be used. The 6 way rotary switch S3 adds extra resistance in series to the timing chain with each rotation, minimum resistance point "a" maximum point "f". The 7555 is wired as an equal mark/space ratio oscillator, the timing resistor chain R1 to R6, being connected back to the output of the timer at pin 3.The output pulse duration is defined